Check out the Gameplay part.
[Edited by Evanscense, 3/26/2012 8:16:38 AM]
It's single player too, however the AI are dumb in many tough situations, so the best solution is to play two players or more.
Anything over normal is rather morbid with 3 AIs to babysit.
Also if you play MP, you can afford to die as your co-op players will be able to revive you. In single player you can only revive the AIs. If you go down, it's back to the checkpoint.
Play it on casual if you want the story in single player. Play it on anything in multi player and have a much better game.