From a regular ol' consumer's perspective (not a "hi-fi" enthusiast), there is nothing inherently wrong with a non-neutral frequency response. Many like a coloured sound, and a headphone with the Beats's frequency response curve could sound amazing. These headphones are for listening to music and maybe DJing, not mastering in the studio (although marketing may suggest otherwise...). Build quality and looks are legitimate concerns, but tend to be overly singled out in these sorts of debates. Sure the Beats are plasticky and absolutely ridiculous looking (to me), but so are many other headphones that don't get anywhere close to the flak that the Beats receive, that may even be highly lauded by those who bash the Beats. Ignore comfort, fashionability, morals and reputation of the company, etc, and just focus on the one prevailing criteria that people use to compare and rank headphones - sound quality - or arguably more important within the Beats's price range, cost/performance ratio.
Beats owners - feel free to justify the price you paid with the fashion symbol reason, but if you're defending your purchase with claims of superior sound quality, give up. You've been played by Noel Lee and Jimmy Iovine. Experienced headphone enthusiasts who have heard the Beats line and much, much more universally say that the Beats don't sound good for their price. You may personally think they sound great for what you paid, but you haven't heard the headphones that those criticising your purchase have heard.
As for my own thoughts, I've only heard the Beats Studio long enough to form a solid opinion, and I think they're worth about $200 less than their $300 Amazon price tag. But I can understand how someone would think the Studios are amazing if their closest reference was a pair of iBuds.