While not first person, Fallout Tactics is pretty sweet, I have been playing it for a few days now, and while very hard, it is very rewarding to have to pay to outfit your squad, and its just a cool enviroment (if you played either of the fallout RPG's, youll understand, if not, go pick up a copy of Fallout, it is one of the best games of all time! 2 was pretty good too, but very repetitive.) and it is multiplayer
Or, if your a battletech/mechwarrior nut like me, Mechwarrior 4 is also very good, I just finished that, hence getting fallout tactics.
I, myself am still waiting for return to wolfenstein, and Duke Nukem forever (SHAKE IT BABY!)[:D]as far as FPS games go.