Sandtrap.

I played 8 hours straight last night. Beat the game with a friend co-op on legendary. Don't do it with four, it's way to easy, even at the most difficult setting. I don't know who said they where disappointed with the ending, but I wasn't. Maybe they didn't do it on legendary? Anyhow if you do beat the game on this setting, wait till after the credits for the real ending.