This is a comment on the major rumors out there that we're getting before 6th ed launch - they could all be false and we don't know all the rules or their interactions. Please read and comment with this in mind.
Allies - lol. Because Games Workshop has proven it can balance one book worth of units against each other regularly across authors and editions. I expect to see a lot of tournaments with: "6th edition rules will be used, no Allies" in their player packs.
Hull points - ah ye poor armies without meltaguns. This could be good or bad depending how it's actually implemented. If it's actual hull points like structure points, not good but it looks more to be like a sort of HP status where if you take X amount of hits (most likely penetrating) you die. This would absolve the issue of "I shook your Rhino 200 times but it didn't die" but isn't really going to solve "meltagun to the facitis" for heavier tanks if they still die to a direct damage result. This could be hugely dependent on how other rules interact with this (though it appears vehicles are now very frightened of combat).
AP for Combat Weapons - same again, good or bad depending how it works. Are power weapons really only AP3? This would make things like Terminators even more of a bother as the like of Power Fists/Thunder Hammers/Chainfists are seen how regularly outside of Imperial armies? If they are AP2, well all good and what precisly was the reason for this change? If there are some other numerous AP3 weapons which weren't getting through power armor before then, well there's that but otherwise the majority of things which died when they got punched in combat now die without a save. Poor non-Marines.
The irony of course would be force weapons become AP2 and power weapons AP3. More GK hate ensues.
More Missions - Always a good thing, particularly since Dawn of War has disappeared into the ether. How they handle the concept of Kill Points though... Regardless, Troops are still important so that's good.
Extra terrain controlled by user - because allowing players to play around with terrain is always a good idea. Some will say this just adds another strategic layer but it opens up a lot of stupid silly concepts *places big ass fortification in front of skimmer army*. Haven't heard anything extra about the terrain effects ala Fantasy but just like Allies, if this is in play I can see it being ignored by most because terrain proactively hurting some armies and not others is good for balance and fun. Random
Charges - we still aren't sure how this will go with lots of systems being chucked out there as rumours. Regardless, without knowing much else (are silly evasion statistics in? Looks like preferred enemy on shooting is - oh hello Wolf Priests and Chaplains, coming out to play? Destroyers, too! Hive Tyrant, you can make those Hive Guard better please.) and 'knowing' cover is going to 5+, is shooting going to take a hit at all? Or are we going to see silly charge ranges akin to Fantasy. We shall see, regardless, we know my thoughts on extra randomness, yes?
Psychic Powers -
Need I say more?
Psychic powers see an increase but it seems unlikely all races will get an even psychic field - fine offensively but defensively? Could hurt though of course "Allies" is supposed to be the miracle system here I imagine...
Anyway, we shall see what everything brings. Only a little while longer now and when pre-orders go up we can all lol at the prices (ya complain about that $75 Americans, complain about that) :P.
Fun times for all!