A big part of the problem is that the market is still in love with the repeated hook and god-awful "crunk" aesthetic. Jay-Z, Kanye, Eminem (although I think he is a lousy human being), and Ludacris are legitimately talented big-time modern rappers. I consider most of the Wu-Tang to be relatively underground, so do not include any of them.
Oh, and I think most of the people griping about Britney's weight should take a walk in the mall. 9 out of 10 people they will see over age 14 are in worse shape than Britney. I think she'll continue to tighten up.