When i first built my PC i got
Far Cry = really good game with excellent environments
HL2 = comes with CSS for hours of online fun, single player is also a good game and good GFX.
Doom 3 & ROE = dark atmospheric and makes you jump in the odd place, a good game IMO.
i also played FEAR, quake 4 and PREY but wasn't as keen on these games. Quake 4 online gave me a few weeks of fun online and the single player is worth playing. FEAR is also OK in single player but i didn't like the online play. I'm currently playing PREY but I'm not to keen on it, I'm not really a fan of weird weapons etc.
Ive yet to play COD 1 and 2 but from the demo of COD 2 i don't think I'll like it.
Mark