Dark Sun. I don't know how well it will translate to 4E, but it's the perfect points of light / realistic setting AFAIK.
No gods, elemental priests instead, perfect for the changes to alignment.
Deal with psionics by giving everyone the half-elf "multi-class" ability (one free at-will power that they use as a per encounter power) call is a mental effect, and you're set.
The cities that stand are ruled by tyrants of pure evil and cunning. They slaughter their own subjects to fuel a ritual that grants them more power. Evil bastards. Some of the backstory is that they chose a race and eradicated it from the face of Athas. All of them, gone. Genocide. Evil bastards.
To make it even better, simply fast forward a few centuries, use the maps for the locations of ancient ruins, and off you go.
EDIT: further, it's also largely unexplored. Only the valley of Tyr was detailed in the setting / novels. A bit outside of that was detailed in the later expansions, but the majority of the planet / plane / whatever are open.
Best setting ever produced.