These headphones are decent, for what they are. If they were 100 or even 120 dollars cheaper, they'd be a great deal and a great pair of headphones. The build quality is what you'd expect from Sennheiser, the battery life is really great, and overall they're quite good.
However, I ran into a few problems when using them with my PC. Number one, after extended use sessions (3-8 hours plus) my ears and the top of my head began to REALLY hurt. The cups on the cans (portion that goes over your ear) are quite small, very difficult to keep comfortably on your ears for any extended periods. Just a slight increase in size would make a world of difference here.
Number two, I found that when using them with my PC especially I received a NUMBER of audio artifacts when listening to anything below lossless or 320kbps quality. Streams, youtube, and most kinds of music created weird audio distortions when I was watching at less than the highest quality settings (audiably speaking).
Finally, last but not least, there's the specific pain it created in the top of my head over time. I don't know if it's the specific mechanism of action squeezing the headphones onto your head, the leather support on the top, or just its specific size compared to my head's, but it would create horrible headaches which would last for hours, as I used these about 6 hours a day.
All that said, if you're looking for something to use on the go with your phone, it's a decent option. If you're looking for any high quality audio...I'd look elsewhere.
PS--other than the long term comfort, if I was using these for only an hour at a time they were quite comfortable (although very hot), and the noise cancelling seemed to mess with audio quality even worse when it's on--and if you're using them wirelessly I found no way to turn the noise cancelling off.