A legendary FPS that you need to play online.
The online play is what makes this game legendary, there are many servers, roughly 400 at one time on v1.16 and roughly 1300 at one time on v1.32. You'll never get bored, and there are many clans to join, people to meet (and frag) and mods to choose. There are 4 different types of match, Deathmatch, Team Deathman, Capture the Flag and Tourney. These are the defaults you get with the game. There are many more with different mods, such as Last Man Standing, and Freeze Tag (which is like Team Deathmatch, but with a twist).
There isn't much more to say about this game, but you must try it at least. It has probably revolutionized online play for FPSs everywhere.
-Zal