I think you guys have this wrong. The gods dont back out of any promise they make.
What Athena says to him at the beginning of GoW 1 that if he kills Ares then 'his past will be forgiven'. Obviously to Kratos, and to the gamer, we assume it to be what Kratos wants. But as we learn its his, and our own, misconception. She never said that she would take away the memories that haunt him. And in the end she says his past is forgiven just as she promised.
But this is important nonetheless since it highlights the fundamental flaw of Kratos: his inability to accept responsibility for this actions and therefore be unable to forgive himself what he did to his family. He can hide behind Ares tricking him, but he still killed his wife and daughter with his own hands. He wants the Gods to erase these memories (nightmares) because he cant accept what he did. He wants to kill himself because maybe that will end everything. But it doesn't. It wont. Its why family becomes a key theme in GoW3, especially with Pandora and Zeus mocking him etc. Kratos is so hellbent on getting revenge, and blaming others etc that he doesnt see who is really at fault: himself. And the final story arc of GoW3 is about this realisation.
Likewise its important to note that Kratos view of the Gods only becomes one of pessimism as the games go on. Where he was once asking Ares for his help, he now feels betrayed and despises what the Gods represent. Not getting what he wanted in GoW is a defining point in him becoming unhinged... its also a defining point in the Gods ultimately sealing their own fate by thinking that can control a man who has suffered like he has suffered by making him a God.
Also I disagree with the idea that he just wants all the gods dead. He just wants Zeus dead. The others just happen to stand in his way. Likewise, Kratos comes to the realisation that power cannot be placed in the hands of the Gods because he knows first hand that it just creates a cycle of control, but also indirectly a cycle of not assuming responsibility for your own actions because man will just worship Gods whenever they need help (this is more metaphorical) . Kratos forgiving himself and reaching this point of accepting what he had down is the ultimate stand against the Gods. He doesnt need them. And he never did. And this is how they lose their power and influence.
When you promise something that the person assumes is X, but you ment Y and never tried to really set it straight you are tricking, manipulating and betraying.
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"