Really, post-apoc which is not Fallout-like, would rock on so many levels. I mean, does it always have to be mutants and deserts? How about a flooded world? Frozen jungles? Underwater? Post-NotLD? Hand of God?
And while I'm at it: Why does the end of the world have to result as just a rotten/torn down form of our old world, government, society and all? There was some tribe culture in FO 2, why not use it more?