Half-Life, Goldeneye, Halo, Unreal Tournament, Quake, Doom, Counterstrike, Deus Ex.
All FPS', all around before Call of Duty. Even if Activision somehow manage to milk Call of Duty to its death, the FPS genre will continue to be popular. There's actually a fair amount of variety out there for FPS', unlike the music genre where the actual gameplay is rather one-dimensional.