Pros: Stable on the head, exquisite feeling, more comfortable than most supra aural headphones, linear, coherent sound, great bass performance,
Cons: Not comfortable enough for long listening sessions, big case, cable coating material and pricey replacement, thin headband padding, expensive
I will get my bias out of the way first: I really enjoy the sound of many Sennheisers, and in my opinion the Momentum Full Size is the best sounding portable I have tried, and the best all-round sounding consumer-targeted portable headphone on the market.
Appearance-wise the Momentum is, as I mentioned, an exquisite feeling headphone. It reminds me of that modernist British industrial design that is the Bowers and Wilkins P5 and P7, but more classic or vintage looking (cough cough hipster) and with aluminum instead of stainless steel. The headphone is basically an aluminum headband with two ear cups fastened on. The headband padding and earpads are made from lamb leather and the ear cup housings are made from glass-filled plastic. The ear cups are tension-adjusted by sliding them up and down on the headband; there is no ratcheting or click adjustment. My Momentums are the black model with red cabling, a black with red stitched carrying case, red stitching on the headband, and red cloth covering the driver baffle plates inside the ear cups. The ear cups are a matte finish, which does concern me about picking up scratches. The cable connecting the left and right channels is the same material as the input cable, and may worry some people as the wires are exposed and may snag on something and tear. As for appearances out on the street, the Momentum doesn't immediately look like a theft magnet or something that shouts "I'm super expensive". It's a bit like the Audi A4 of portable headphones. At first sight it might look like a much cheaper-priced retro style headphone like the Panasonic RP-HTX7, and to me adds to its value of being able to be used in public. Overall I wouldn't say the Momentum Full Size isn't as sturdy as the V-Moda Crossfade M100 or the XS, and the padding due to the delicate leather material is less durable than the Alcanatara on the Momentum On Ear. But the earpads are replaceable.
The cable is a mixed bag for me. Sure it's a good looker, has a metal fob with 3 button iOS controls, a good microphone, and an aluminum jack with a 90 degrees of movement variable adjusting plug. But the rubber coating the cable is thin and develops kinks rather easily. I am also concerned about the lack of strain reliefs on the terminations to the ear cup, the input connector, and the remote fob. But after a couple accidental tugs rest assured there was no breaking and the connector simply detached from my phone. As for spares, the Momentum does come with a plain spare straight cable, but with no remote and no variable angle jack. And because the cables terminate to a 2.5mm connector on the ear cup with a bayonet lock, getting a replacement should you destroy the iOS cable requires you to buy a genuine Sennheiser cable at a cost of 70 dollars, or 50 dollars for the Momentum On Ear cable that has no metal fob body and a 90 degree fixed angle jack. Ouch.
On the bright side there are plenty of manufactures (usually from China) on Ebay offering aftermarket cables made specifically to be compatible with the Momentum's 2.5mm connector, with iOS controls for a much lower price than a genuine one. And if you want to go crazy, I believe there are some cables purchasable for the Momentum made from pure silver or copper and silver. For an arm and a leg of course. The case is nylon coated, has a sturdy zipper, is padded inside with a hook and loop pocket to store your cable, but it's big in size and requires you to push the ear cups all the way to their top positions in order for them to fit into the slots.
Now onto comfort. The headband padding is rather hard and splits into two rails. This can cause some digging into the scalp if the headphones are not adjusted properly. I usually sit them flat on the top of my head and am usually fine. The headphone is also rather light so this helps. The Momentum was advertised initially as an around-ear headphone, but for most people it isn't. The ear cups are simply not wide and tall enough for most peoples' ears. I find that the hard cartilaginous areas of my ear tuck inside the cups and rest against the cloth inner walls, but the bottom of the pads rest on top of my earlobes. I have big ears, so if I don't adjust the cups just right, I find the hard areas of my ears pressing against the plastic baffle plates, which can hurt over time. Since they still fit around the larger areas of my ears, they are more stable and won't just slip off, but since they are very cozy and squeeze the edges of my ears, I find that I have to take the Momentums off every hour or so to let my ears breathe, and then I can put them back on and resume listening. Prolonged wear without a break causes my ears to become hot, sore and pinched. In my opinion, this is the biggest drawback that can spoil the overall experience of the Momentums and their initially lofty 350 to 400 US dollar price tag. They sound so good that you will want to listen to them for hours on end, but your ears will likely object to this prolonged listening session.
And finally the sound.
I purchased the Momentum Full Size after briefly owning the Momentum On Ear and returning it due to not liking its signature. I found the On Ear to not only make my ears red hot and sore from as little as a half hour of wearing time, the treble was too splashy, the mid bass too overbearing and the vocals too withdrawn and the headphone rather unsatisfactory for genres other than pop, hip-hop, trance, dance and harder hitting house music. The Full Size Momentum is a much different sounding headphone. The Momentum to my ears has a linear enough response that from bottom end to the lower treble, there is plenty of information portrayed. If one looks at the frequency chart, the Momentum has an almost flat curve from the sub bass to the lower treble, where it begins to roll off. Now some people will argue that the Momentum is slow, muffled, and bass heavy. I argue that the people who say that are likely treble heads. For you guys I recommend the Bowers and Wilkins P7.
There isn't an up front treble that gives the Momentum an immediately forward and sparkly sound. So it may sound shelved in the vocal range or slightly echoey. But once your ears adjust to the sound signature, you will find that they have a sound that goes well with almost every genre. The treble still has plenty of detail, but is never harsh. To me it's more subdued than it is softer.
The mids have a liquid sort of sound to them that while they may seem polite, have plenty of energy in the vocals. The upper mids have a little bit of a glare or splash to them that may become blarey at higher volumes with trumpets, saxophones, and female singers, but for most of the music I listen to (soul, smooth jazz, Spanish guitar work, Japanese electronica, baroque, pop rock, house, hip-hop, Arabic pop and drum and bass), this isn't much of an issue.
The bass is really where the Momentums shine. The bass from the lower bass to the upper bass has excellent presence, impact, detail and is never overblown. The mid bass to my ears has a bit of that Sennheiser wooden-like bloominess (like the HD650) that makes it a tad loose, but it never becomes one-note or droning like the Momentum On Ear became. The upper bass blends into the lower mids excellently without adding an overly chesty sound like the Audio-Technica ATH-M50 did to my ears, or adding too much forwardness to already forward mids, making the headphone sound honky (like the V-Moda XS). The sub bass is done exceptionally well. It has plenty of tightness, rumbles when it needs to (for drums and hip-hop) quick decay (the notes don't hang around and sound muddy), and isn't overemphasized. So it doesn't sound boomy, slow, loose or overly rumbly. The bass to my ears on the Momentum is exceptionally coherent. It doesn't have an overboosted upper bass with a woeful bottom end, making it sound honky or overly warm at times (like the AKG K240 Studio/MKII). It doesn't have a droning, over boosted mid bass like the Momentum On Ear. And it doesn't have a conspicuously powerful sub bass with a thin upper mid bass and sucked out upper bass, making it sound overly bottom heavy with an unnatural and lean transition to the midrange (like the Beyerdynamic DT990 Pro 250 on a solid state amp, the Sennheiser HD380 Pro, and Beyerdynamic Custom One Pro).
Sound character-wise, the Momentum reminds me of a closed back, slightly less hi-fi HD650 with a more boosted bottom end, a slightly less forward midrange and more shelved off-sounding vocals. If black on the Momentum isn't for you, there are two other color options. There is brown Momentum with oliveish/coffee brown colored padding and satin-finished cups, and the ivory Momentum with tan ear cups, medium brown headband, and black earpads and black padding inside the headband. I have read that with cleaning the leather on the brown Momentum can turn black or darker after a while. So if this is a concern, the black Momentum or ivory version with their black inside (i.e. the parts that touch your scalp and ears) padding may be a better choice. In retrospect, I wish I chose the ivory Momentum over the black model due to looks with my phone being white, but the black model is still a good looker, and probably blends in better with my blackish hair.
Quick comparison with the Sony MDR-1R
The Momentum has a more impactful, fairly forward, and harder hitting sound than the Sony MDR-1R, which is a headphone with a more dreamy, sweeter, diffuse midrange, wider soundstage imaging, a softer treble, and a bass that dives off after the upper mid bass. The MDR-1R has a distinctly Japanese-style sound tuning (politer, laid back and tuned more by the ear), whereas the Momentum has more of an ear and frequency measurement-tuned sound. It's a more German sound but with warmth. The MDR-1R is softer and much more of a polite, relax-with-music-in-the-background sort of sound; whereas the Momentum is a more forward, demands-to-be-up-front sound, with a subdued treble. One suits a listening mood more than the other. While the 1R is more relaxing to listen to and more comfortable to wear, the Momentum grabs my attention more and is a funner listening experience.