While these phones don't have active noise cancellation, they do provide very good isolation from noise. In addition, they are the most comfortable headphones I've ever used, bar none. In particular, the headband is very well padded. When you're bald like me, that's important. ;-)
And to answer an earlier question, they're very comfortable when worn over glasses. I've watched three-hour movies while wearing these phones without feeling any discomfort--and that's something I can't say about any other headphones I've owned (and I've tried a lot over the years).
Sound quality? Hey, I'm no golden-ears audiophile, but they sound excellent to me for both music and videos. I paid $150 for a pair of these a couple of months ago, and they were worth it. At this price, they're a steal.