Sixth Edition is different. However, in many ways, it's also very much the same, but it's those niggling details that are going to catch you and trip you up. Because of that, I'm using this post as both a listing of all the changes from 5E that I saw on my first read through the book as well as a running commentary on things.
It's not intended to be an evaluation of anything or any kind of "this is good, this is bad" assessment- it's still way too early for that. Whatever opinions I may voice here are tentative; there's a good chance that many of them will shift a lot before the month is out.
If you see something you think I missed that is important, feel free to bring it up- discussion on this subject is good. I don't doubt there are things that slipped by my attention and chances are I'm going to read the book three or five more times before I have any kind of good grasp on it.
Obviously premeasuring is a thing now. You can always measure any time whenever for whatever reason.
Models within a unit with different speeds can all move full speed as long as they stay in coherency. Big boon for jump packs and cavalry/beasts.
One model in a unit moving no longer makes the whole unit count as moving (at least for shooting purposes.) That's very nice.
The shooting player chooses the order the wound pool is resolved in, but must resolve all wounds of a given type at the same time. So if you have two Plasma and four Bolter wounds, you can do either one first, but you can't do one Plasma, then the Bolters, then the other Plasma.
Instant Death now works off of your modified Toughness.
Look Out, Sir only applies with models from the same unit, which is different from its Fantasy version.
A unit Gone to Ground can still fire snap shots. That's... pretty good, actually.
Cover saves are model-by-model now, which is actually kinda unfortunate. You're going to see a lot more bickering about whether models have cover.
Focus Fire occurs before you make any rolls to hit. Interesting.
You can't charge units you can't see. Not a huge deal, but relevant sometimes.
Charge moves still happen at the speed of the slowest model in the unit, which is no surprise.
Pile-In moves can trigger dangerous terrain tests. I think this is a change?
In addition to being worse with regards to Overwatch and Disordered Charges (i.e. no +1A), when multi-assaulting you can only go after a secondary charge target if you are unable to reach your primary target. This makes charging multiple units much, MUCH harder.
The Trapped! rule has been clarified to be a little more understandable. Still functions the same and will basically never come up, though.
Regrouping is now done if you at at 25% or more, not 50%. Big change for non-Marines. Also like in Fantasy double-ones will allow even understrength units to regroup. And you can even regroup if not in coherency now! However, if you regroup you can ONLY fire Snap Shots. (Edit: and if you have an IC with you you can ignore the 25% restriction.) There are also no restrictions on regrouping within 6" of the enemy or when out of coherency.
If you charge a unit that is falling back and they fail their test to regroup, you still move forward before removing them as a casualty. (In multiple assaults you pretend they don't exist, though.)
Ha ha, Assault Vehicle has a special exception in there so that even if the tank dies that turn the unit can still assault. Oh, GW.
Barrages pull casualties from the center of the blast. That... is very awkward, especially with a multiple barrage, because you will have to differentiate each shot to determine where casualties are pulled from. Oh, and no more "durf multiple barrage only applies if I'm shooting two guns" nonsense. Sorry, Manticore, you're a fucking multiple barrage.
Blind is a pretty cool rule, since it actually makes Initiative relevant. Harsh penalties, also.
Concussive actually reduces your initiative value. Interesting.
You can't Go to Ground if you're Fearless. Boo-urns.
Eternal Warrior would seem to allow you to take FNP saves against ID wounds now.
Fleet lets you reroll one or more of the dice when making a charge or run move. That... is actually a lot more relevant because you can turn your 4+1 charge into 4+(something) instead and just keep the good result. I take back some of my previous complaints about the semi-irrelevance of Fleet.
Your battlements are not considered impassible terrain for Deep Strike (but the enemy's are.) I'm not entirely sure what that means but it seems like it might be important.
Force Weapons work like GK NFW now, activating to make all their wounds cause ID.
Furious Charge is a special exception such that you don't get the bonus when making a Disordered Charge, so that isn't a general rule for effects that trigger when you charge. That's... good. However, the loss of the +1I bonus is pretty unkind.
Hammer of Wrath hits are unmodified strength and AP-, awww.
Haywire is no longer an additional roll above and beyond its strength vs AV penetration roll. Minor nerf on something that got way, way better.
Interceptor is an interesting rule, since it lets you shoot at all types of targets if you have Skyfire. (Normally Skyfire must Snap Shot to shoot at ground targets.) Will be interesting to see who/what gets it, aside from the terrain pieces.
It Will Not Die is basically a more-differenter regeneration. If Tyranids get super-lucky they will be able to have both. *fingers crossed*
Missile Lock is a really good rule, but, uh, who gets it? And why does it only apply to Missiles?
Move Through Cover doesn't help you when charging into cover at all- you still roll three dice and drop the highest. Uh... what the hell?
One guy with Night Vision lets the whole squad ignore Night Fight. Kinda sweet.
Poison thankfully keeps the reroll if your Str is better than their Tough AND you use your best wound number- so a Trygon with Toxin now wounds on a 2+ with reroll against most things. Sexy.
Preferred Enemy likewise applies to the whole unit if a single member has it. And, of course, it works on both shooting and melee, which is very nice.
Rampage is also a fairly neat rule, but... who gets it?
Scout is redeploying, not movement. No more Scouting for cover saves, guys. Also, you can't disembark as part of a Scout move.
Shrouded not only gives you +2 to your cover save but gives you a 5+ if you didn't have one. Very good.
Skilled Rider is +1 to your Jink save. Again, very nice. However, it's weird they didn't standardize the language for improving cover saves... although, given it's GW, maybe that isn't so weird.
Slow and Purposeful prevents Sweeping Advance and Run moves as well as Flat Out (though I wonder if there will be any tanks with SnP.) Also it stops you from making Overwatch shots, which is pretty hurtful.
Smash halves your attacks characteristic, but you still get (or don't get) the bonuses from other sources, so charging, etc, is applied after. Tervigons are the kings of Smashing, since they have an odd number of attacks and a low strength. Two S10 attacks that reroll failed wounds thanks to poison? Yes, please. You can't Smash with HoW hits (nor does it make them AP2), but you can reroll ANY penetration roll- so you can try and upgrade a glance to a pen if you want to and if you're really weird you can try and turn a pen into a failure.
Soul Blaze is a pretty mediocre rule (AP5 doesn't scare many people), but it is just kinda tagged on to all the Pyromancy powers, so I guess that's okay. Note it triggers at the end of each turn, meaning each player turn- twice as much burnination.
Thunder Hammer + Lightning Claw gives you an extra attack now. Because, um, I guess they're both unwieldy and stuff. Meh.
Split Fire is an awkward rule and I dread how it will be applied to Tau. Takes a Ld test, only works on one model, etc.
Stealth is culmulative with Shrouded, which will give you a 4+ cover save no matter what and usually better than that.
Strikedown has a really awkward wording, but it appears to apply to you if you pass or fail a save against it. (Except that FNP lets you ignore the wound, so you neither passed a save nor suffered wound... what the hell?) In any case it's a pretty decent rule, since it lets you strike before them and slows them down if you're not in CC. Note that it is a model-by-model thing (though the Diff Terrain part will effectively apply to the whole unit.)
Supersonic Flyers can't hover. Very relevant.
Swarms lose Stealth but ignore difficult terrain now. Big nerf to Scarabs there. The doubled wounds from blasts/templates is also worded differently and now applies to unsaved wounds specifically, so you'll roll cover/armor first and then double wounds (and remove bases to ID if applicable.)
Tank Hunter gives you a reroll to pen now rather than +1. Considering how rare the rule is this won't have much effect, but in most cases it is a downgrade, since you commonly saw it used to make something able to glance/penetrate a tank when it otherwise couldn't.
Twin-linked blasts can't reroll hits in an attempt to scatter anymore. Meh?
Vector Strike works on anything (even fliers) but is done at unmodified strength, so no Smashing. It hits side armor, which will make some tanks a lot harder to hurt with it.
Bikes can't Go to Ground at all anymore, but do have Jink now.
Artillery guns are now T7 W2 models with 3+ rather than being the kookiest tanks around. Independent Characters in an Artillery unit can't shoot at a different target anymore. You use the T7 of the guns so long as there are any guns remaining at all, so they're actually kinda super hard to wound now. Weird... from one of the most fragile unit types to one of the toughest.
Jump Packs can save their jumpiness for the assault (rather than movement) phase, and if they do they get to reroll the charge distance and get the Hammer of Wrath impact hits as well as ignoring terrain in the usual manner. (edited)
Cavalry and Beasts are different now. That's something, I guess.
When Swooping with a Flying MC, you have to move at least 12" and must do like a flyer, pivoting 90 degrees and moving in a straight line. Flying MCs that Swoop don't have to take Dangerous Terrain tests... but MCs always pass such tests anyways (due to Move Through Cover.) If you Swoop, your Run move is upgraded to 2d6" and you can't be charged at all, which is something. Despite their limited movement arc they can still shoot 360. Blasts and templates can't hit them, same as flyers. You can fly off the board, which will occasionally be useful so that you aren't shot to death (flyby some dudes with Vector Strike and then go invisible for their turn!) You can Dive (like Going to Ground, sorta) gaining a 5+ cover save, but you can only Snap Shot next turn. But, uh, since you can still charge, so what? Getting knocked to ground when hit (not wounded) really sucks, so you'll see a lot of "shoot all my Bolters at you to knock you down then here come Lascannons" stuff happening. Also, you take a S9 hit with no armor/cover, so having an invuln is a huge deal for MCs.
Pistol give you nothing but an extra attack in CC. I guess Plasma sucks at short range or something?
Models with two Pistols can shoot them both now. Huh, I guess some of my BA guys are now modeled wrong.
Salvo weapons are... weird. They basically use the second profile as Heavy and the first (half range, half shots) as Rapid Fire. Also, the example gun is a weapon that no one has so far.
Weapons have been consolidated into types now, a process that started several years ago and has slowly become more and more comprehensive.
Stub Gun is back in the game, bitches! It's the worst weapon there is- S3 AP- 12" range! Well, okay, maybe not as bad as a Transdimensional Beamer, but still pretty bad.
Chainfists are only AP2, as are their companion weapons (Fists, Eviscerators, etc.) Chainswords are AP-, which alleviates a lot of my concerns about melee sucking for xenos races.
Force Staves are pretty derpy compared to the other types. Gonna have to remodel some dudes, I'm thinking.
Power weapons with "unique rules" (i.e. like every one of them that isn't Imperial) are treated as AP3 weapons. Uh-oh, Terminators are gonna be beasts.
Witchblades are S3+2d6 against tanks now. Not quite so murderously ridiculous.
Nonstandard grenades can't be thrown. Suck on it, Grey Knights.
All grenades hit walkers using Weapon Skill, which makes them a lot less useless.
You can try and use Plasma and Krak Grenades on MCs now. I guess they're awesome against Harpies?
If you're within 8" of someone and have Defensive Grenades, you get Stealth. Kooky. For some reason they refused to use the Disordered Charge term with these even though it does almost exactly the same thing.
Meltabombs are AP1 in assault now, which is nice. They can't be thrown, though.
Characters get to allocate wounds on a six to hit, both in shooting and CC. Sarges got a lot better, especially Long Fang sarges (who can take special weapons.)
If you aren't engaged, you can't issue a challenge; careful about keeping that sarge at the back of the fight. While in a challenge you are only consider to be in B2B witht he guy you're fighting, so no swinging your chainsword in a glistening arc (of essence?) and hitting everyone around you.
You get a reroll for every five buddies watching if your enemy in a challenge is alone, which can be on whatever you want in the fight. Sending a lone dude to kill one guy in an enemy squad can be kinda risky.
You can't Flat Out with a Tank Shock anymore. Eldar players everywhere cry.
Vehicle shooting from multiple weapons works out cover separately from each weapon, which makes the issue of Psyfleman shooting extra-complicated.
Everyone knows the damage table is pretty different, but there are some interesting details. Shaken and Stunned both allow you to fire Snap Shots- so suppressing a tank is only partially effective, although against most big-gun tanks (Russes, etc) it prevents them from firing their main cannon due to being unable to Snap Shot blast weapons. Weapon Destroyed kills a random gun, which makes taking out the main cannon of a battle tank much less probable on the first shot (and gives you a reason to buy upgrade guns.) Weapon Destroyed upgrades to Immobilized if you have no guns, but an already-Immobile tank that gets it again loses TWO Hull Points from the shot.
AP1 and AP2 give their bonuses on the table, as undoubtedly everyone has heard. This means a (relative) upgrade to weapons such as Lascannons and Lances.
Cover saves on tanks are taking against glances and pens just as they were before, not before the penetration roll is made as was implied by some sources.
You can't charge a vehicle that you can't hurt in any way. Huh. No more surrounding a Land Raider with Termagants, I guess.
Tanks can't Overwatch. That's good, had been weighing on me for a while.
Glances are worth one combat rez, pens are worth two. It's possible to lose a combat to a normal tank if a special rule or other effect causes wounds on you (Flechette Discharger, Truesilver Hull, etc.)
Shots on a vehicle squadron hit the closest vehicle first and are resolve against it until it is destroyed and then move to the next closest, as with other wound allocation. Combined with the ability to individually move Flat Out or pop Smoke, it means you can often shield yourself with one tank to deny the enemy to ability to affect others in the squad.
You can abandon Immobilized squadronmates and rather than dying, they just act as a separate unit for the rest of the game. Suddenly squads don't suck so much anymore.
Units inside a transport are Fearless. I guess this is basically the same as the way it actually worked before?
Embarking works the same- you can even embark on a tank that moved more than 6", and you just have to get within 2" of its access points.
When disembarking, you start in base with the vehicle and must end WHOLLY within six inches of it- no more benefit for large bases. If you emergency disembark you still get your 6" move, but can't do anything else. You also can't charge out of a vehicle (unless it is assault or open-topped), even if it stood still. Also, you can't disembark from a tank that Tank Shocked- getting surrounded in CC is very problematic for transports.
You can shoot Overwatch out the top of your tank if it gets assaulted. That's pretty badass.
Guys in a Shaken tank can only Snap Shot; ones inside a Stunned tank can't shoot at all. If your ride gets wrecked, you disembark but only get to "move" three inches, rather than six; explodes still puts you right where the tank was. You still have to test Pinning afterwards. There doesn't seem to be any exception for the unit exiting the tank and being able to then shoot/etc, but the wording is a bit unclear.
Flyers coming in from reserves after Zooming off the board must Zoom that turn.
Immobilized flyers must continue going the same speed (combat or cruising) that they were going and can't Evade (for the 5+ jink) or Flat Out any more. However, it can still make its 90 degree turn before moving, so it's not all that limiting. It does stop you from ever disembarking from it unless it has a special rule (like the Ven/Valk/Storm), though, since you have to keep Zooming every turn.
A destroyed flyer comes down as a S6 large blast and doesn't leave any terrain behind; models inside take a S10 no-saves hit and are placed within 3" of the blast marker.
Flyers can always choose to be Skyfire (or not) if they want to be, so one of the best ways to counter a flyer is another flyer.
You can't fire more than two of your missiles on any given turn (Bloodstrike, etc.) They don't seem to really have any other rules. One wonders whether this applies to the Seeker Missiles on a Skyray, but presumably not.
The Chariot type (which currently is just the Necron Command Barge) is a bit different; for example, since Flat Out moves aren't done during the movement phase, it cuts down the range you can Sweep someone at a fair bit. More importantly a Chariot can assault (whaaaaa) and you get +1 armor save while staying on board it. You also get d6 S6 Hammer of Wrath hits with the Chariot which, combined with the rider's attacks, ends up being pretty hardcore.
Walkers that get immobilized are hit on the rear armor; it makes grinding down a Dread a bit easier of a process. They also still get the -1A penalty for this, as before.
Walkers can't Death or Glory when Rammed, but if they live through the hit they can fight the tank in CC that turn.
You can shoot after ramming now, but since you have to move full speed you can only Snap Shot. Skimmers also are easier to ram, since they only get their Jink save against it.
Smoke is now done in the shooting, not movement, phase.
"Permeable" walls are now the default rather than the rulebook telling us to decide for ourselves. Thank the lord.
You can take armor saves against dangerous terrain now. That makes it... a lot less dangerous. However, you can be forced to take multiple tests in a phase if you move through multiple pieces.
There's a new terrain type, "lethal" terrain, that is basically just impassible (except that if you end on it for any reason you die.) Stops jumpers/skimmers from hanging off it, I suppose.
Going to Ground in area terrain gives you +2 to your cover save rather than +1.
Guys inside buildings take one wound (no cover saves) for each damage result rolled on it, but you can't shoot at an empty one to preemptively destroy it. They also have their own unique damage table now, which is as follows: -1 AV, shaken (and can only disembark 3"), d6 S6 wounds (no cover), 2d6 such hits and kill one weapon on the building, -d3 armor and kill one weapon, 2d6 of the hits and anyone inside must get out (and it's now impassible), as above but 4d6 hits and a S4 d6" blast from the building. Low-AP weapons give the usual bonuses on the table (which, it should be noted, goes up to seven, not six.)
You can jump off of battlements (tops of buildings) and ruins now, ha ha. It's... pretty lethal, but if maybe you absolutely have to get away from the enemy...
Automated weapons on a building "always fire at BS2." Does that override the BS1 of Snap Firing at flyers, etc?
Buildings that are not bought as part of an army have their AVs reduced by two and can't shoot their guns. This sets a new record for lowest AV starting (seven!) and makes said buildings a lot less scary for armies like 'Nids or others with weak AT.
Ruins with bases are area terrain. Ruins are 4+ cover. Going to Ground gives you +2 to your cover in area terrain. Guardsmen in a ruin are fucking bosses.
Shooting within a ruin measures distance base-to-base, not to other parts of the model. I don't believe this had been clarified before. Coherency, however, is much more flexible (giving you a 6" space when on different levels.)
Beasts can now enter the upper levels of ruins (though cavalry can't.) Walkers and MCs get an annoying "maybe, if it looks sturdy" exception, which is going to cause problems.
Hills, Ruins, Barricades, and other "heavy" terrain maintain their 4+ save. That's a good thing, at least. Vehicle wrecks are still 5+, though other wreckage is 4+.
The changes to missions, deployments, and all of that are so important they're going to get a whole post of their own, but long story short: deployments favor shooting, missions are mostly about objectives now, though killing is still valuable. You can't control more than one objective with a single unit, you can't control an objective if you're in a tank/building (or are a vehicle yourself.) Vehicles (and Swarms) also can't contest ("deny" in the new terminology) objectives to the enemy.
You can't hold more than half your army in reserve, though units forced to start there (flyers, Drop Pods, etc) don't count. Reserves always arrive on a 3+, regardless of turn number, and a result of '1' on the die always fails. If you can't move far enough to get on the board from reserves (Immobilized on terrain, bad Diff Terrain test, etc) you move the minimum distance needed to get on the board rather than being destroyed.
You can't charge when coming in from reserves, though presumably Ymgarl Genestealers and some other units will get exceptions to that.
Overall Thoughts
Striking at higher initiative is super-clutch now that casualties are pulled from the front. It's more an issue for large units, but it will apply pretty regularly to everyone. 3" pile-ins also make getting large units into a fight a lot harder.
Positioning models properly is now the most important skill in 40K.
6E is very bloody- tanks and infantry alike will be dying in droves due to lower saves, etc.
Things are much more mobile and you have more options for how to move with almost every unit.
