I gotta say it...
Ya know I checked Forgotten Realms as a kind of knee-jerk vote... but I think on reflection I would probably be less excited to play in a Dark Sun campaign than any of the others.
I thought the basic premise of the setting was good enough, but a lot of the ideas were were just way too 'out there' (i.e., transforming into a 'good' or a 'bad' dragon if you were a wizard, IIRC).
The worst part for me was the munchkinity of it all. First time we ever saw 10th level spells, I believe. I'm sure it would have put FR to shame, if it had ever become as popular.