The Sony NC200Ds' left earcup features a Monitor button alongside the Artificial Intelligence switch that allows you to hear what's going on outside your 'phones without taking them off. Of course, you could always just slip them off your ears and let them rest on your neck, but it's comforting to know that the feature exists, and it works.
Overall, I liked the sound of the headphones, though it's worth noting that I actually liked the sound slightly better with the noise cancellation turned off. The bass goes deep with plenty of definition, and voices appear natural with adequate volume extending into the louder ranges.
On the downside, to enhance the detail, the treble is slightly overemphasized and a bit too sizzly. These are what we call "bright" headphones and can lead to listening fatigue with some people over extended listening sessions, like in an airplane or a long car ride.
Other small quibbles include an audible hiss from the noise canceling that takes a little of the warmth out the bass and midrange (vocals). The headphones also sound a touch more hollow (canned) and less open with noise cancellation engaged.
In all, though, there's a lot to like here. Excellent design, flavorful sound, and these guys cost $100 less than the Bose QuietComfort 15. At $200, they're not cheap, but comparatively speaking, they're reasonably priced and worth checking out if you're in the market for a pair of noise-canceling headphones.