Originally Posted by DArtagnan 
The best kind of dungeon is one that tells a story. It's the dungeon that represents an experience in itself.
Fallout 3, for instance, handles this very well.
I agree, FO3 did have some great buildings and underground areas in that regard. Although ironically a lot of them were very samey in terms of visuals. It was the placement of miscellaneous items (bodies, notes, etc.) that gave them a nice touch.