I have the NC300Ds and I've used them a lot for about a year. If you want a Sony and it has to have noise cancelling, I think, it is the best option. Anyway, I think, whether you'll like them, or not, will depend mostly on the kind of noise, you want to filter out. For low-pitched noise, like airplane engines, it works pretty well and the sound quality is relatively good overall, but pure noise-isolating earphones (I've personally tried ones from Shure, Westone and Etymotic) without noise cancelling electronics in the same price range are better. Compared to those, the NC300D tends to sound slightly muffled and there is some degree of hissing, especially with the stock eartips and the "general purpose" noise cancelling mode.
The Sony silicone tips are really bad at isolating noise. That means, speech and other higher-pitched noise passes almost unfiltered, because the noise cancelling is fairly good at low frequencies but doesn't help much for higher pitched, variable noise. The phones do get better with some good foam or triple-flange tips, but overall you should be really sure, you need active noise cancelling and know what it can and can't do, otherwise you'll probably be happier with a noise isolating phone, because for most kinds of everyday noise, the active noise cancelling in the NC300D does not make a huge difference and I've yet to see an active noise canceller, that does not sacrifice sound quality to some degree.
Edited by EvilMadEngineer - 2/11/13 at 5:53pm