The boys from ID have been so kind as to release Wolfenstein “Enemy Territory”, a completely free, fully functional online 3D shooter taking after their Return to Castle Wolfenstein game.
Check it out if you’re into online shooters like Medal of Honour and Call of Duty, and you’ll probably like it.
Gameplay is mainly aimed at teamplay (so no dull running around and just shooting peeps), so you actually have to think a bit while you run around and shoot peeps. The game also lets you select what “class” (medic, engineer, soldier..) you’ll be playing, and you get experience points from staying alive and doing what you’re supposed to do.
Don’t forget to install the patch though, or you’ll have a hard time finding servers running the game.