Metro 2033
I played through a few hours of this last night and I just had to post here and recommend it. I'm a sucker for single player FPS games with great atmosphere and immersion, and this fits the bill perfectly. The graphics really are beautiful - some of the best lighting and shadowing effects i've ever seen, better than even Crysis. It really gives my graphics card quite the work out.
It's kinda like STALKER (and maybe FEAR) in its creepy atmosphere, but without all the bugs and glitches and with better production value overall. Less open and less-RPG-like, more linear and cinematic (in-game, not pre-rendered custscenes everywhere), like the Half-Life games.
Also - and this is very important to me - 3D Vision works perfectly with this game, and it makes the experience that much more intense!
*EDIT* Well, I have to say, i'm pretty disappointed in this game. After the initial "Wow" factor any strong buzz, the game really just isnt that fun to play. Something about the hit detection and performance dips just makes it unpleasant to play for me anymore.