I actually thing the complete opposite is true. This is the game Tim has always wanted to make, but didn't think he'd be able to. Selling out doesn't enter into it at all - Tim is not bowing to publisher pressure or making the game he thinks there is a bigger market demand for. In fact, if you read some articles\interviews about the game, Tim mentions that some publishers wanted to tone down his ideas (I think one even suggested ditching the metal-oriented universe all-together). No, this is not Tim conforming or selling out in any way. This is Tim finding himself with an opportunity to unleash and flesh out his longest lasting desires as a game designer, and as a result I'm inclined to believe that all the elements that make Tim' games uniquely his, particularly the fresh creativity of his ideas, will be at their absolute strongest.
Brutal Legend may just be.... The Ultimate Tim Game™.
Until he thinks of a better one, of course.
It's true that many violent games exist without any other redeeming features or value... but surely that will never be true for a game which Tim is at the helm of... For that to be true, he would have to abandon everything that makes him a great game designer, and that would be rather pointless for everyone involved, don't you think?
I personally think it's funny how everyone's trying get all buddy-buddy with Schafer's mind, calling him "Tim" like they know him personally and then writing out all his inner motives. Not that I think you guys are wrong. I just think its interesting.