Standard disclaimers are applicable here.
Looking at the storm shield, it seems pretty obvious what we gained. Instead of a 4+ invulnerable save that could only be used in close combat, we gained a 3+ invulnerable save that could be used against anything thrown our way. What's not to like about that?
How are we going to take what is amazing, and put it in our lists? That is the more difficult question. We need to look at what this piece of wargear provides an unit. The most obvious one, is durability. Pointing low AP weaponry or power weapons at someone wearing a SS doesn't phase them much. Sure, eventually they'll fail the 3+ invulnerable save, but they've got a pretty good chance of passing it too. Just having a couple SS's makes the whole unit so much more survivable.
What else do they do for us? They give us wound allocation funsies! Much like the humble Neophyte, taking these gives us a differing model in an unit so we can split our incoming wounds up before rolling armor saves. This ensures we don't have to mass-roll all of our wounds against the whole unit. By doing this, perhaps some of the unit will live to see another day!
Okay, so we know what these things do now. Before we move on, it is important to note that they did receive a price increase to compensate for their improved status. Basically, anyone trying to take one from the Armory has to pay 15 points instead 10 points, as before. Our Assault Squads had their SS price increased from 3 points to 15 points. This effectively makes them unusable in Assault Squads, but I'll get into that in a sec.
That is all well and good, but we need to know how to use them in our forces. I'll start with our independent characters. Our commanders will get great use out of this piece of wargear for a couple of reasons. The first, they don't have an invulnerable save built in like the Chaplain or the newer renditions in other SM codices. We have the Iron Halo option in the codex, which is a 4+ save, but you can only take one per army. Obviously, it is a much worse save in comparison to the storm shield. However, the iron halo doesn't take a hand to use, so you can still gain an additional attack for having two close combat weapons. But you need to decide if that extra attack is worth decreasing the save and taking an extra 10 point hit. I don't think it is. You can easily arm, for example, a Marshal with a Lightning Claw and a Storm Shield to maintain his combat effectiveness while giving him extreme durability. It works because the commander has the wounds to give. While he'll still get an instant death against high strength weapons (he's in a squad anyway), he'll be able to shrug off a great many power weapon hits.
However, I would avoid putting this piece of wargear on our other ICs due to their lackluster performance in most lists. The Chaplain is really only effective in Black Tide lists (which makes use of Righteous Zeal) so you don't want to prevent wounds to your huge squads. In addition, he already has an invulnerable save available to him, so there is no point in paying more points for something he already has. They are expensive enough as it is. As for the Techmarine, he is a complete waste of space in our codex in my opinion. He doesn't feature any worthwhile weaponry, his statline is not impressive at all, and is extremely expensive for what you get. Not only that, he takes up a valuable elite slot.
I also mentioned that Assault Squads could take Storm Shields. Some players have jumped up and down in celebration at this combination. I don't understand why. To take an Assault Squad Initiate with a Storm Shield, you're paying 38 points for a single guy. Yikes! All you get is a jump pack dude with 2 standard attacks on the charge. Not impressive at all. You could buy a terminator for that and they would be much more effective in close combat.
One of the arguments supporting the use of this type of squad is that its highly mobile and "durable". That it can easily move around the board and tie up important CC-units in your opponent's army. There is a problem with that. Pre-FAQ, they were easy to eliminate because they needed to be fielded in small numbers to be cost effective. This would be even more so with SS's in the unit. Because of this, your opponent only has to make you fail five, count them, FIVE 3+ armor saves to wipe them off the map. Because they are packing power armor at best, you cannot rely on shrugging off even a small amount of incoming fire. Then your expensive little tar-pit unit is dead, or is no longer effective at the role you put it in your army for. Torrent of fire will easily kill this unit and storm shields do nothing to prevent that. So don't try to make a bad unit good with an expensive upgrade!
Now, we come to an unit that many of us have already used quite frequently. The Assault Terminator unit. The optimal squad ratio before the FAQ was 3 LC and 2 TH/SS terminators with Furious Charge. I don't believe this ratio needs to change. You're still killing almost everything on the charge with the lightning claws. However, now, your TH/SS terminators give the unit the ability to survive incoming assaults from dedicated assault units. This was something that they couldn't cope with before, opening up a more broad set of tactics to use in your battles.
They can also survive a good deal of incoming fire if their LRC gets shot from under them; long enough to perhaps slog their way into combat. None of this is really "new" so to speak, but we did gain the ability to field full TH/SS terminator squads. Unfortunately, they were not useful in our lists because the storm shields didn't work against shooting. But now they do, with an increased save to top it off. This setup can be an useful tool in armies who need a counter-assault element in their forces, though it isn't as effective as our Vanilla SM brethren due to combat squading. They also have the advantage of having a Librarian being able to move them around at will. These types of terminators also function well as a tarpit unit and if they survive to strike back, something is going to die. :)
I don't want to get too long winded here in this article, but I do want to end the article with a thought. The improvement of the armor save is extremely nice to have in our armies, as it gives units the ability to take more punishment before succumbing. However, I do not entirely believe that these units lend themselves to effective ultra-competitive lists. Do they work well in competitive lists in a casual environment? Sure. But don't jump the gun here and include SS terminators in every army simply because of the upgrade. You still need to build balance and synergy into your lists. If they fit the list, take them. But if they stick out like a sore thumb, re-examine what you're trying to do with your list and make some adjustments.
With that being said, I'm trying to develop some lists that might fall into the balanced, competitive realm. We'll just have to see if I come up with something good. :)
The BT FAQ: What did we really get? Part One
The BT FAQ: What did we really get? Part Two