While they're certainly increasing in technical complexity, I just haven't felt like first-person shooters have been thinking bigger for...quite a long time.
When you think back to Thief, Hitman, System Shock, and Deus Ex, those games were pretty nuts in terms of how much scope they had for the time, and how many things you could do, and how you could use their mechanics and systems. I guess some would make the argument that the games had so much complexity that the games became unwieldy or clumsy to play, but I think it is more than worth it.
When I look at what those series' have become, most of them are, at best, the same game like a decade later. Some of them are much simpler (Hitman: Absolution comes to mind). In either case, they don't seem to be thinking bigger. Is there just not much more that developers could cram into an FPS without it becoming full-on Fallout 3 and more of an RPG than a shooter?
Sure, there are indie/off-beat games doing weird stuff in FPS games, but I doubt it's ever going to start some new zeitgeist in the FPS genre. Receiver and ARMA have a high degree of specificity in one area, though they don't have the same kind of scope as the other games I mentioned. And uhhhh, Zeno Clash lets you shoot weird crossbows and spearguns made out of animal bone and shell and whatever, and then you barely use them because the game is actually a brawler, so I'll award points to them for doing something weird. Still, those things are not really raising the bar on the genre as a whole.