For the price, these headphones have incredible sound quality. Compared to other headphones like the HD 650, this is by no means an 'inferior' headphone just different. Superb soundstage and bass and treble capabilities. out of the box the highs mids and lows are well balanced. 
 
Comfort is 5 stars, light and comfy. The headband is pleather, don't know if it will discolour/rot off over time. Some reports that the wood is real but I doubt it. Absolutely love the retro premium style to bits, needs to win an award for one of the best looking headphones. I took off half a star for design because of cracking for early batches and Sennheiser public commitment to replace defective units within 2 years (nothing special, just honoring warranty nothing more). Also you need to be careful with the the metal grill, it will bend and dent very very easily so you need to baby these headphones. Buy a case/pouch/bag for it and put it away after use.
 
For the price I have no negative points to pick other than perhaps the cable could be ended with a 3.5mm because with the adaptor it might stress your audio port. To address this I bought a gold plated extension cable.
 
Many people talk about amping this headphone but I see absolutely no need for it. Without additional amping the sounds are great no distortion at all. I tried with a 100ohm Amp with no significant improvement. I will try with a 300ohm amp since the frequency charts tells us the bass improves with that level.
 
Overall, I'm very happy with these headphones and they compliment the closed-back portable Sennheiser Momentum very well. 

 
The Momentum have a great classic retro quality style and fantastic sound to boot. Out of the box, the headphones are setup for a great listening experience for a majority of my music including R&B, classical, rock, Jazz, 80's, 90's, trance. Of couse, with a DSP you can tune it to your liking and the Momentum handles it very well. The case, although big, offers the protection it deserves. Not sure how Senn could have done that differently. Something unadvertised is the "noise-isolation" resulting from the ear cups - it actually works just as well (if not better) than some digital noise cancelling units. Yes, the ear cup sits on the ear and will touch the circumference, this is by design and offers the noise-isolation whilst being smaller and more practical.
 
The only gripe I have is that the connectors are not gold plated.
 
Quite frankly, I was blown away by these 'cans', very happy indeed. In my view - straight into the Hall of Fame for these.
 
>> I can't reply to comments below for some reason, I'll try to reply by editing this review <<
 
EDIT 1: The unit comes with two cables - one with and one without the inline remote which I thought was a useful touch. I walk around with these headphones and listen to them whilst on the move indoors and outdoors. Prospective buyers should be fully aware of the "context-of-use" before buying these. For example, if you are considering the Senn HD 650 then they are a completely different headphone for just sit down and listen. Please be aware of this when comparing headphones. The earpads are made from a high-quality english lambs leather. Yes, not Pleather that will rot away after awhile but the softest lamb leather you could imagine. I cannot imagine how anyone can get these headphones around-the-ear unless you are a tiny dwarf, and trust me I've seen dwarfs with large ears so these are definitely around-on-ear hybrid. I use the headphones with a software DSP and playback of lossless/hq-mp3 files on an iPhone. A DSP can seriously improve listening experience and these headphones are highly capable across the frequency spectrum. I have never felt I wish it could have more bass/treble. It's just right for me. If you try these headphones in the shop you might notice the weak volume (i know i did). Just check "sound-check" and "volume limits" are off. I have great hearing and 70% volume gives a pleasant listening experience.