**SPOILER ALERT**
Actually, I'm replaying God of War 2 right now to get platinum trophy, and I think the whole revenge on Zeus thing was really Kratos being manipulated into thinking he needed to do that by Gaia.
Think about it: God of War 1 - Kratos is promised by Athena he'd be forgiven for his sins if he kills Ares since Ares is being a douche. He kills Ares, then he is forgiven, but "forgiven" doesn't mean "your conscience will stop bugging you", so he tries to commit suicide since he can't live with himself. Athena stops him from doing that and instead crown him the new God of War (Not a really bright idea in my opinion, but meh)
Then in the beginning of God of War 2 the narrator tells us basically that Kratos, as the new God of War is being a douche (almost the same as Ares was). So then Zeus kills him. Kratos is being pulled by the arms of Hades or what not, and then Gaia comes along and says something along the lines of "Stop being such a coward and kill Zeus!".
Que Kratos's revenge journey upon Zeus.
So then in God of War 3 when Gaia allegedly betrays Kratos, she tells him "you were just a pawn" - and that he was, they Titans helped him so he could ressurect them. nothing more.
They neglected to notice that by the time he ressurected them, he was so obssesed with his revenge, that he forgot why it all started.
tl;dr: Gaia is a manipulative b***h.
