I think I'll post my idea of what I'll think the story of GoW 3 will be like.
It starts out with Kratos fighting his way up the titans backs. He is going along fighting the god of Olympus. Hades escapes after Kratos kills Posiedon. He eventually get to the top and fights Zeus. After he kills him, he learns that the Titans betrayed him, and just use him kill Zeus. Gaia kills him and gets sent back to the Hades (again) and he escapes (again) with the help of the gravedigger from GoW 1. He goes around fighting the Titans, who have taken over the gods roles. The titans, however, have not been good rulers of the world. Kratos goes around killing them all until he gets to Gaia. He fights her in an epic battle. He kills her, but as she dies, she falls on him, just like the Collosus of Rhodes did in 2. Hades, who is alive, comes up to him and says that Zeus was a bad ruler and he wanted him gone. He thanks him and lets him die in peace, and spend eternity in the place with his wife and daughter (Ellysium I think).