If you don't own Red Orchestra then get on steam and download that motherfucker. It's one of the most fun fps games I've played in a while. It's pretty damn realistic as far as fps' go, with stuff like realistic penetration of tank armor and limping if shot in the leg. Things can also get pretty intense on a full server as the max amount of players in a game is 50.
So if you're looking for an awesome fps with a steep learning curve, download Red Orchestra: Osfront 41-45 off of Steam.
