I also received my pair today.
First impressions are decent, certainly a lot less bassy than I was expecting from some of the discussion. Doesn't bleed into the mids much, and on they subject of midrange, they are quite clear, better than I thought they would be. Highs are a bit rolled off. Essentially, they follow the Sennheiser house sound relatively closely.
Regarding comfort, they are great for my ears. Quite lightweight and the leather is very supple. Their size is smaller than I was expecting, but they are still comfortably circumaural for me (I wouldn't say tight tight fit, but they don't leave a lot of space). I can definitely see this being an issue for people with large ears.
Still, as a quick comparison with the Sony MDR-Z1000 (which I believe some people have been asking for), the MOMENTUM frequency reproduction is very slightly bassier and has a noticeably weaker upper end. The biggest thing I've noticed so far though, is that the Z1000s are miles ahead in resolving power. Comparatively, the MOMENTUMs sound blurred and sluggish, though maybe this is partially expected as the Sennheisers are clearly being marketed as a style headphone with good sound coming along for the ride.
On the plus side, the MOMENTUMs are much more portable, due their smaller size, lighter weight, and slimmer profile on one's head. Good for a portable setup, but for a more trans/semi portable setup I can't help but feel there must be better options.
Maybe it's just my ears, maybe it's just something about today, or maybe the Z1000s just tickle me in all the right spots, but as I listen to the Sennheisers right now I just have this strong feeling deep in my soul to reach over and grab my Sonys or even my HD580s!
I know I sound real critical here, but they're not actually horrible. If style and portability are important, these are probably worth a look; they're absolutely gorgeous and supremely comfortable.
I'll hold off on a final declaration of what I think of the Sennheiser MOMENTUM for now. I'll give them a bit more head time first, but at this point I think my pair will have their own For Sale thread before long.
For reference, about 90% of my listening so far has been through my Opus DAC and CKKIII amp, foobar WASAPI output, 320kbps and FLAC files.
Edited by earthpeople - 9/19/12 at 9:33pm