Sound Quality is amazing, music can be listened to at much lower volumes due to excellent noise cancellations, with no music playing these could almost be used as ear muffs.
Volume can go so high that they can almost be used as mini speakers.
Build Quality is very good, cable is coiled and thick so is unlikely to break.
Headphones can be folded for transport, although are big so not ideal for travelling with.
Have had mine a few years now and still work perfectly.
My only complaint with them is that your head does get quite hot after wearing them for a while and this can be uncomfortable.
To summarise, brilliant headphones although not great everyday headphones, I use mine for long car journeys and chilling out in my room. For on the move I use Sennheiser PMX 200 headphones.