All of the source powered games. And, well just about every FPS I can get my hands on, especially both Stalker games. I play a lot of FSX, I especially like it because I'm veerrrryyy slowly getting my pilots license. RPG's are good too, but since Diablo II I've been let down, even Fallout 3 I gave up on.....
Right now I play LFS, a few demo's, always trying new demo's, Stalker Clear Sky and Shadow of Chernobyl. Fallout 3, but as I said I'm getting really bored, Left4Dead, CSS...ET, ETQW. Man I have a ton of games, I guess I'm truly happy online in an FPS owning, got the headset on, hopefully a sound server and ping and I'm good.
I absolytely love Simulation, so LFS and FSX are very important and taken seriously, while FPS online is semi-serious, tons of fun tho. RPG, can't explain it, very rewarding in a different way, like a good book, I suppose that's how it should be?