One thing I really like about Crysis 2 is the posthuman element. Post/transhumanism seems like a terrific concept to pursue for science fiction action games. I think Deus Ex and Crysis 2 are the only games I can recall that actually go over the transition of humanity (or elements thereof) into something greater. Other games, such Halo, do feature transhumanism. But unlike Deus Ex and Crysis 2, it doesn't concern itself with the transition, which is the element I find most fascinating.
It's becoming a Sci-Fi fetish of mine.