Pros: Clarity, clarity, clarity! Detail, neutrality, revealing, maybe even transparent? Very comfortable.
Cons: You will definitely hear the flaws in bad recordings
So, I've finally found MY headphones :) I tried the Sennheiser Momentum, the KEF M500, B&W P7, Sony MDR 1R, Philips Fidelio L2 (yes, the L2), the B&O H6, the Focal Spirit Classic (you read that right too) and the Sony MDR Z1000.
I was in search of a good sounding, but most of all comfortable closed headphone. All the headphones I've tried above sounded quite good, but none of them were comfortable enough for me (except for the Z1000, which is the 7520's less refined brother) so I ended up returning all of them.
So what was the first thing I noticed when I listened to the 7520? The amazing clarity. I'm not exaggerating when I say that all the above headphones (with the exception of maybe the L2) sound veiled compared to the 7520. Also the level of detail these headphones retrieve is amazing. It's actually leaning towards the analytical side, without losing it's musicality. I can listen to music for hours without the level of detail becoming too much, but when I want to close my eyes and focus on the music there is just oodles of detail to be found, I just get lost in the music :)
To my ears this headphone responds very well throughout the entire frequency range. The highs are nice and crisp but never sound harsh. Sometimes you will hear a bit of sibilance though, but that's only with less well mastered recordings. The mids are very neutral and detailed. And the bass is very very nicely done, very taught, controlled, and again I think fairly neutral. And it will still reach deep into sub-bass regions when the music calls for it. If a song is warm, the headphone will sound warm. If a song is cold, it'll sound cold. If the music is rocking, these headphones will rock. If the music is serene and quiet, these headphones will be very composed.
The soundstage of these headphones is also quite good. I'd say it portrays the soundstage the way the audio engineer intended it to sound (provided he was using good speakers/headphones as well of course :)). So with classical music the soundstage can sound quite wide, and with other music it can sound quite narrow, depending on how it's recorded. I also feel like the imaging is done very well and the instrumental separation is excellent. When you focus you can and will hear every individual instrument, easily. And if you don't want to focus, it turns into a nice ensemble so you can just do what music is intended for: enjoyment :)
The Z1000 is the 7520's brother. They look exactly the same, just that the Z1000 has silver accents. I think they also use the same drivers as the technical specs are exactly the same, but others have pointed out that they are actually different drivers with very similar specs. Whatever the case is, they certainly do not sound the same. The bass response is a bit rolled off I'd say on the Z1000. It's just not there, even when the music calls for it. And compared to the 7520 the soundstaging was less expansive when the music called for it. The rest of the frequency range sounded otherwise fairly similar.
These headphones put a smile on my face when I listen to music. Eventhough they are marketed to the professional audio engineer market (and I can certainly hear why), I think any audiophile will be able to appreciate these headphones. I've never heard a truly neutral high-end headphone, so I cannot compare it to that, but I think this is quite close to a neutral sounding headphone.
I highly recommend this headphone to you all. At least give it a listen :)
Edit 3/25/2014: I lowered the rating by half a star as there is a bit of creaking in the headphone that I haven't been able to fix. It occurs when I move my head or jaw. It can be quite annoying. The SQ is still superb, but the creaking sometimes distracts me from my listening.