Music composers Timothy Williams and Tyler Bates(main composer) have been attached to the game. Williams verified that he's working on orchestration and aditional music. Perfect! The music is in the works. But my concern is the story and the characters. By the way, I'm sad that Gerard K. Marino is not mentioned, hopefully he'll be back.
http://multiplayerblog.mtv.com/2012/01/04/composers-resume-confirms-existence-of-god-of-war-4/
Co-op is also said to be rumored buuuuuuuuuuuuuuut really? Is highly unnecessary if there is co-op. Deimos is mentioned....and he's dead. So that's just old news in my opinion.