Based on my quick impression, the Beats ($399) version was the best headphone I heard that did a big subwoofer like bass. I think they are great if you are a bass head and like your electronic dance music or hiphop. There were some headphones that offer similar amount of bass, but none sounded as good as those Beats imo in terms of quality. ( i didn't compare it to all headphones that exist ofcourse, just the headphones that were on display )
If you like mids, detail, high, soundstage, imaging, comfort, durability and so on ..... don't buy these headphones. For bass heads with enough money to spend, I can see why people buy these. I personally would never ever buy them since my Shure SRH 1840 costed only $50 more and I got a subwoofer at home with my speakers that beats the Beats in terms of bass.
For the right people (bass heads), I think these Beats headphones are quite good.
But I can understand the hate, since my $99 Shure SE215 probably sounds better. I didn't A/B directly as I just listened to it for a couple of minutes in a shop.