OK, so here are my impressions.
My previous headset was a Hyper X Cloud, so that is the basis of my comparison.
Sound: Overall, sound of the headsets is pretty similar to my ear. I actually think the Hyper-X has a bigger bass response than the Sennheisers, but that the Sennheisers have an overall clearer/more accurate sound. The HUGE difference though, is that these Sennheisers have an open can design, as opposed to a closed back. This is, in my opinion a good thing. I can hear my own voice when I'm talking, which is nice. Also, the sounds just seem more "natural," if that makes sense. The closed back design of most other sets DOES do a better job blocking out ambient sound, so in that way, the Sennheiser isn't as good if you're in a noisy place. Also, there's more sound-leak to your environment when using an open back design. Still, I feel like
Mic: This mic is far better than the old boom mic on my Hyper X set. First off, the noise canceling is much better; it picks up less of my typing noise and breathing and ambient stuff. Secondly, the muting by raising the boom is fantastically convenient. Lastly (perhaps most importantly) the voice quality it creates is more natural and less nasally/cell phone sounding than other mics I've used in the past.
Comfort: The velour texture of the ear cups and the headband is very soft, cushiony and pleasant. Haven't done any marathon gaming in them, but seem very up to the task. They are pretty light-weight, for what that is worth.
Look: I love the all-black look. They don't scream "1337 haxor gamer," but rather a more subdued, cool look. Obviously, this is subjective.
Nice touches: I love the raise to mute boom, super convenient and intuitive. Also great: the on headphone volume wheel on the right can. Cable is fabric wrapped, and generously long, not needing an extension.
Overall: I'm very happy with this set, and feel like it is a meaningful upgrade to my previous set. I hope you all get yours and enjoy them as much as I am.