Favourite RPG Setting
To look at this setiously, I'd have to consider the first settings I encountered that really took steps in unusual directions.
That brings us to Dark Sun and Planescape. Evocative artwork, strange twists on the familiar races and tropes, new ideas.
To look at this non-seriously, I love the subversive layers upon layers of Paranoia's Alpha Complex.
Combining the two... HōL
I probably could have reached HōL if I combined shelf inches of books...where the two biggest collections are the crazy, gonzo of Rifts, and the dark, atmosphere of World of Darkness.
Dark, crazy, gonzo, dripping with atmosphere = HōL
This question didn't ask for the most coherent game.