I love Fallout, but my favorite post-apocalyptic setting has to be one where "The apocalypse" never actually happened, but instead life is still mostly gone. Something outside of nature destroying humanity, or humanity destroying itself happened-- but the landscape would imply exactly that. for other, possibly sinister reasons, like... the singularity making it so that all populated planets are abandoned and everyone goes to a dyson sphere computer to upload their brains into their own perfect dream bubble.

Like the blood red LCL sea at End of Evangelion.