Pros: Warm, smooth and engaging high fidelity audio. Gorgeous design with quality materials. Very comfortable (for me). Very light.
Cons: Slightly excessive mid-bass and laid-back top-end may turn off purists. Soundstage isn't great. Remote volume up/down only usable on i-devices.
On sound alone, the Sennheiser Momentums are worth every penny. But aside from being wonderful sounding, the elegant design is beautiful and luxuriant with stainless steel band, real leather and quality plastic cups in a nice, dark bronze finish. The standard cable is also very high quality, with a substantial metal remote attached to it.
The case isn't as large and bulky as I expected from reviews, and it's sturdy enough to keep the headphones safe under most circumstances.
They are very comfortable. The light weight and the materials inside the earcups ensure the fit is great, with minimal headband pressure and without heating up your ears. The cups are on the small side, so if you have large ears you can expect a tight fit. Isolation is very good, not class leading but good enough to shut out most unwanted noises.
Sound wise, Sennheiser really nailed this one. The Momentum is one of the best sounding portable headphones available at any price; they even are good enough to be compared to the better sounding sealed headphones out there meant for home use. I've been through most of the competition from Logitech, Ultrasone (specifically, the ED8), Sony, AKG, B&W, Focal etc and the only headphones I've heard that actually better the Momentum on audio quality alone are the recently released KEF M500s and B&W P7s.
The sound of the Momentum is a little on the mellow side, with a mid-bass presence definitely (but tastefully) north of neutral and a treble to the other way around. And it's actually a good tonal balance for a portable headphone; because when out and about a bass boost is preferred in most scenarios, and the laid-back treble makes the Momentum forgiving with poorer recordings. But the great thing is that the bass isn't TOO much and the treble isn't TOO laid-back. And the Momentum has very good clarity so while the tonality is definitely dark and mellow, details and upper harmonics don't get completely smeared as there is plenty of detail resolution available. Putting aside the ups and downs (literally) at the frequency extremes, the Momentum is a very transparent sounding headphone.
While always with a slightly thick texture, the bass of the Momentum is well defined and quite tight for a sealed headphone. Extension is very good and it doesn't feel very bloated or slow. And the treble is very good for a portable headphone, too. It has its issues, but for most people I think it will be appreciated, especially as it's so forgiving.
And the midrange is among the very best I've heard from portable headphones. Rich, natural, yummy and open sounding. While the headphone does lack some soundstage depth and therefore can sound a little congested overall, the midrange itself on the Momentum doesn't feel closed in at all. The midrange transits into the treble very well. I have issues with the slight thickness due to the bass and the lack of upper midrange air and presence due to the recessed treble. But other than that, things sounds very nice and inviting.
With the Momentum, Sennheiser made the ideal on-the-go headphone. You get a transparent and natural sound that you can listen to for hours and that suits portable use, and you get this great sound in a portable, comfortable, practical and beautiful package.
Great job, Sennheiser!