^a key point in the petition, is if they "wait to complain", it will be too late. You complain about small things in a near finished product, like balance, things missing from the UI, spell tree layout. Not the art direction. Frankly, its already probably too late.
I don't mind the new look, and on first glance thought it just seemed very "blizzard" in style... it reminded me of color use in Starcraft and Warcraft games... but, admittedly, while I liked it, I didn't think that this looked like a Diablo game.
My experience with Diablo, was mainly from Diablo 2, and Lord of Destruction. The characters were in proportion, seemed to be intended to be realistic, had no customization, and the environments were dark, dirty, and gothic. It all added up to a certain atmosphere, that currently Diablo III does not have.
I credit this to Blizzard taking the art direction of Diablo to a broader audience.... and I don't like the sellout attitude.
I have many questions for Blizzard on this one... for starters: Why in the living **** are there female barbarians in Diablo III? Why are the character models cartoonish? Why are the armor and weapons exaggerated? Why do the textures look like they were made by oil pastels? What happened to the light radius? Are you merging the Diablo and Warcraft franchises? Do I get to play as an Orc?
If I wanted a cartoon Diablo clone with pastel textures, I'd just play Mythos... its going to be free, and apparently has some ex-Diablo programmers working on the project.