The Quake series of FPS was the one that got the most amount of fans to the genre. Quake II was the one that got them hooked.
Weapons galore and enough enemies to shoot up, a seemingly endless amount of time can be spent on this classic game. First Person Shooter fans should already have this game, but if they do not, they should.
If you are not one of those people that don't like all of the gore and blood, do not, I repeat DO NOT get this game.