I used to poo poo PCs fighting gods. I used to think it was over the top munchkin silliness. I think playing games with larger than life but serious heroes - like Exalted and Scion - changed my opinion of that.
In any case, 4e is the first edition where I find the prospect of fighting a deity to be extremely interesting. The epic tier truly changes the tone of the game. Here the PCs battle against transcendent threats to all existence, with everything hanging in the balance. At this stage, they are beyond legend - they are the stuff of myth.