Yes, it was lacking any story whatsoever, but from what I remember (it's been a while) the singleplayer levels were very well designed, fairly nonlinear and had

Yes, it was lacking any story whatsoever, but from what I remember (it's been a while) the singleplayer levels were very well designed, fairly nonlinear and had tons of secrets. (Still, the real meat was in the multiplayer, of course)