Here's a pretty good interview about the art direction. Jay Wilson makes a good comment on how the game direction doesn't start out all apocalyptic, but it works it's way there. It's pretty much what I was guessing the game was going to be like. Which is why I told some people "Just wait until the game actually gets to hell". I mean, people didn't really expect the whole game to look like the first 2 areas we've seen, did they?
http://kotaku.com/5031732/art-apocalypse-blizzards-wilson-talks-diablo-iii-design-decisions