OK, first things first - The noise cancellation isn't as good as the Bose QC15... but for about a third of the price, what do you expect? They do work well, and are effective at cutting out a large amount of background noise (through a combination of passive isolation and active noise cancelling). They are good enough to allow enjoyment of classical music on trains and planes, and work well at cutting out background hum (e.g. air conditioning) in an office environment. Like all noise cancelling headphones, they are pretty ineffective against human voices - so no good for cutting out annoying office mates! Whereas with the Bose QC15 you feel like you are inside a silent bubble, with these there is still some background noise audible. But for the price they are a very good buy. The sound quality is very good, and about what you'd expect for any headphones around this price point - i.e. not as detailed as a pair of high-end hifi headphones, but perfectly enjoyable for any kind of listening including rock or classical. They are not bass-heavy, so they are give a good, honest sound.
As long as you have reasonable expectations of the capabilities of noise cancellation (and don't compare them with the much more expensive Bose), you won't be disappointed.
UPDATE (June 2015): Well, after a year of occasional use, the headband has cracked on both sides, rendering the headphones useless. Poor design and choice of materials to blame. I would have expected better even at this price point. Hence I have deducted 1 star from my original 4* review.