Noise cancellation on the Q20i is 5/5 as in the best I've experienced so far (I've owned the QC15 and two other noise canceling ones that cost $40 and $100). I don't mean it's silent, but it's marginally better than the QC15 and a world apart from the cheaper ones.

Sound quality is 3.5/5 - it's not audiophile, but above average. The reason I have them isn't for mind-blowing sound quality, and it isn't for image or any such nonsense (I think Bose home audio is a horrendous deal for example); it's simply the best noise cancellation out there.