Single Player Coop

Oh, and single player coop (while probably really difficult to do, and twice the amount of work) is a really cool idea for a game. Like Resident Evil 4 with Ashley, or ICO with the princess. It helps put a different spin on things, being able to always have someone going with the character. Kind of what they do in Half Life 2, where all of the characters with you flesh out the story, and keep you company.