Daern's Instant Fortress

Many people in 40K are wondering "Are my shields prepared to face the power of this fully-functional battlestation?" Which is to say, what is up with fortifications and does my army need them/can my army handle them? Obviously this is going to vary from one fortification to another, but the truth is that they aren't particularly game-breaking and many of the "strategies" that are being recommended with them ("Buy two Fortresses and use them to block off your deployment zone!") are downright idiotic.

Fortifications are specialized tools that let you trade a non-insignificant number of points for some survivability and specialized firepower. Some armies can benefit from these things, others not so much so- so let's take a look at what they each do and what they offer us.
Aegis Defense Line

This is the one that has everyone talking, but it's got a bunch of caveats to go with it. First of all, it's pretty limited in what it does- while you can stretch it a pretty fair ways if you just lay them out end to end, that is often going to be pretty awkward/inconvenient/nonfeasible because of existent terrain. (Yes, I am aware the rulebook tells you to place fortifications before terrain, but tournaments are probably going to reject this system- reshuffling the terrain every round creates too many problems.) You can easily end up walling yourself into your own deployment zone and, for infantry at least, the walls are tall enough that it won't be hard for the enemy to end up getting cover saves from them as well unless you're standing right up to the edge.

Those are the downsides. The upside? 50pts for 24"+ of 4+ cover save terrain that goes where you need it. It's even tall enough to give cover to most transports and even some larger tanks (though not skimmers), making it a real blessing for mech armies despite them being unable to use the "go to ground for a 2+" feature. Being able to place some terrain around midfield, where you plan to lay an objective or three, or deep in your zone to protect a backfield shooting is a very powerful effect. Especially if your local area tends to have sparse fields of battle you may want to grab some Aegis walls to cover yourself.

The add-ons are a little trickier. The Comms Relay can give you rerolls on your reserves for a cheap 20pts, so long as you can dedicate a unit to manning it- for flyer-based or other reserve armies that lack good reserve manipulation this can be very handy. However, the inability to take the other guns often makes this option less attractive, as they're pretty good. The Icarus Lascannon has a board-wide reach and Skyfire/Interceptor, giving it a good chance to at least significantly damage a flyer as it enters the board- while its numbers work out to be worse than the Quad Gun overall, it is cheaper and thus less likely simply be wasted points. The Quad Gun has a nominally shorter range but puts out a Rifleman worth of firepower (dependent on your army's BS, of course) and is easily one of the strongest ways to shoot down aerial units, as flyers are all AV10, 11, or 12.

The real question with the Aegis line is: how much is this going to help me? Oftentimes, the answer is "not enough on its own"- this single anti-flyer emplacement does not a good defense against such an army make, as "real" flyer armies are going to bring 4-6 (or occasionally more) such targets to the field. So maybe you get lucky and the Aegis shoots down one... and the other five will blast it off the map and then shred the rest of your army piece by piece. And destroying is certainly quite possible- T7/W2/3+ is somewhat durable, but probably not enough to shrug off dedicated fire, so expect a lone Aegis to go down quickly. Now, if you have additional support units to hit them with, it becomes a lot more useful- the saturation principle in action again.

Skyshield Landing Pad

Well, it's not too expensive at 75pts and, unlike the others, it doesn't have any upgrades to throw onto it. So what's it do? It... uh... it's a thing. You can have it either in shield mode (which gives all units on the upper layer a 4++) or unfurled mode (which makes you not scatter when you DS onto it.) So.... yeah. It can give you a vague defensive bonus if you climb into an awkward position or it can make your Deep Strike super reliable... so long as you want to come down in one fairly useless place. And spend a bunch of points.

If it gave you some actual reserve bonuses (like the Comms Relay does) or had guns or could protect some dudes or something it might maybe be worthwhile, but unless you have a magical need to DS a ton of guys into one particular spot, it just isn't very good.

Oh, wait, some of you are bringing up the Chaos Daemons and writing angry responses. Are you going to place your whole army on top of the Landing Pad to get shot at? Everything, concentrated in one easily-avoidable section of the board? For a melee army? Really? I guess... uh... go ahead and do that, then.

Imperial Bastion

Well, it's AV14, that's a pretty huge start. It can hold twenty guys inside (with at least one fire point in each direction), and a significant number more on top. And it's got a Heavy Bolter in each direction as well, just in case. It's also a pretty big, blocky piece of terrain that can easily hide a number of models behind it or give cover saves to large vehicles/MCs. That, in itself, is not all too shabby for 75pts, though also maybe not that great- you're going to need to position it such that it's far enough forward to affect the fight but far enough back that it doesn't get assaulted/melta'd out of the game and cause a ton of wounds to the guys inside.

*edited*
On further reading and discussion, the Quad Gun/Icarus seem to be separate targets that do not benefit from the AV of the building, although this is not entirely clear- it depends on differentiating between "emplaced weapons" and "weapon emplacements." Can the Heavy Bolters be targeted separately? I had assumed not, but the verbiage is so similar it lends a possibility that doing so would work. I think an FAQ would definitely be in order.

G.I. Joe Cobra Command Center Playset
Fortress of Redemption

Because if you're going to take a fortification, you might as well have one that takes up half of your side of the table and gets in the way of absolutely everything. The PlaysetFortress is a massive, four-piece (not three-piece, despite what it says in several places) series of buildings, all toting AV14 and multiple guns/fire points. Two "bunkers" each bring a powerful gun (TLIcarus and large blast barrage Frag shot) with the ability to bolt on some more Heavy Bolters if you feel the need, or upgrade the missiles to have a Krak shot as well. The central "walkway" sports a half dozen fire points (and, like all the pieces, has battlements for units to fight from as well) and the central tower itself is high enough to offer an unrivaled view of the battlefield, even in the face of large blocking terrain pieces. It clocks in at a costly 220 base, up to 290 with all the fixin's, which is a pretty huge chunk of most armies out there.

Why would you want this thing? Well situated decently into your deployment zone and with the "walkway" given a good lane of fire to the surrounding field, it can dispense an incredibly volume of fire from highly-protected firing positions; the PlaysetFortress itself also offers a large hunk of terrain behind which to hide artillery and other barrage weapons. Which army has tons of fragile infantry that can shoot at range, others that want good firing positions, and have lots of indirect bombardment weapons? Hrm, which one could it be?

Oh yes, that's right- Orks.

I kid, but several of the long-range shooting armies, including IG, Tau, SM, and even, yes, some Ork builds can do interesting things with the having a huge block of stuff to get int the way. Is it good? Oh no, oh god no, but that doesn't mean it's awful.

(Addendum: Some people are awfully worked up about the ability to take one of these and "block" a back corner of a table, in theory denying the enemy the ability to get to whatever is back there, such as an objective. A couple problems with this: it involves putting the PlaysetFortress somewhere that is probably non-ideal for lines of sight, it lets you score ONE objective, and it doesn't work against people with good ways to break AV14- which is to say almost everyone. So yeah, go ahead and do your little 400+pt gimmick to take one objective; I'll be over here claiming the other five and making you keep your head down. Oh, and if I wreck it your units disembark through the back door and are now stuck back there for the rest of the game with no LOS to anything and no ability to move. Enjoy!)

Overall Thoughts

There are really only two worthwhile fortification pieces in the game right now, and they're both AV14. It will be interesting if we see some more varied pieces get added in- AV13, 12, or even lower at reduced prices could add some interesting choices for some races, especially if they come with special abilities more complicated than "it exists and can be sat in." For the time being, however, they're really just purchasable terrain that can give you a minimum of flyer defense to go with other stuff you're already bringing- and for some armies that is pretty useful, as even a Vendetta doesn't have very good chances to actually kill AV14 in a single turn.