It's got to be space/trading/combat games for me. I cut my teeth on Elite back in the eighties and I still haven't found anything that feels the same. Xbeyond frontier, Freelancer, homeworld, I don't know why but they just don't seem to cut it. Maybe it's like your first kiss, or first car and nothing will recapture that moment.
I've heard rumours that David Braden one of the creators of Elite is working on Elite 4. Anyone know of this is true? Man I hope so.
the best FPS fighting game for the pc is Novalogics : Joint Operations Typhoon Rising. but only with the fee Mod from brutal-arts.com. game requires your system to be high spec though. barton 2500+, 1gig pc3200, nvidia 6600gt minimum!
Halo, first version, is more a single player game, with online multiplayer being a low res version!!! or at least it was when i bothered to have it installed. i finished it on the xbox, got it for the pc, decided i couldn't be bothered to go for days and finish it on this too although i did used to host online games frequently for it , so have a lot of experience setting the games up
Area 51 -fps similar to Halo - but your actions are dictated by orders or the action of team of whom you have no control -lots of secret bits found by continuous trial and error which does get annoying. If it had the same approach as eg. Desert Storm, it would be a better game.