are you looking at a game with high replay value? I like wolfenstein..but there's not much to do once u beat it...maybe look into some RTS? they seem to offer a good replay value
If you like the realistic aspect of BF2, then I could suggest ARMA II. Still has a few issues to be ironed out but the game is pretty amazing, and the mutliplayer is unrivaled in terms of scope and different missions to play.
Great class-based shooter with heavy emphasis on teamwork. The artsy style IMO makes the game look fresh where as more realistic games show their age down the road.
It's also only 20 bucks off Steam! But if you haven't ever played Half-Life 2, buy the orange box (which includes TF2, Portal, Half-Life 2 with both follow up episodes), it's only 30 bucks and it'll be the best 30 bucks you ever payed for a video game.
I recommend Fallout 3 . Easily get 100+ hours into it, especially with all the expansions out now. If you wanna wait a little while, you can get the Collectors Edition that includes the game + all expansions for $50, instead of paying $40-50 for the game, and then $10 for each expansion. Modern Warfare 2 is also coming out soon.