One word impression of the MDR-Z7:
Terrible.
More later.
Alright, maybe terrible is a tad harsh, but hear me out.
They're way too dark. This one is self explanatory. They have poor treble extension which causes things to sound muffled and sometimes veiled. It also takes away that sense of "air" you get from certain headphones. "Feel the air" is definitely not a good marketing slogan for these.
Their bass is bad. It's at times aggressively hot and gives me headaches. It's too warm and lacks definition. Very soft and muddy. It also doesn't have nearly as good bass extension as their grandfather, which is unacceptable in this day and age. My bass standards/preferences are probably much different from most people, so take this part with a grain of salt I guess.
Their presentation is poor. This is, almost literally, a closed MA900. Let me explain what's wrong with that. With the cups restricting the soundstage width, it causes the center channel of the MDR-Z7 to feel compressed. The staging is plenty deep, but the left and right are being compressed towards it. Essentially what this equates to is an intangible, confused sphere of sound that sounds like it's coming out of a tunnel or a tin can. Very artificial sounding.
They suck the life out of everything I throw at them. This one is a bit more abstract. Something about the combination of the muddy bass, lack of air, and presentation manages to make music sound dead. Vocals have no intricacy or finesse to them. Subtle imaging ques are absent. The timbre of instruments is completely off. These do not make music, they make noise. Overly bassy, dull, compressed noise. Consumers will probably adore these. Audiophiles should look elsewhere.
Build quality is absolutely fantastic. This is one of the nicest looking, nicest feeling headphones I've held in a long time. Comfort is equally superb (though the pads get hot).
Please note that these are impressions on a modded MDR-Z7. After taking the mods out, everything became worse.
Other than the negatives they have decent separation and sound relatively smooth, but that's ONLY after mods. Their grandfather, the Sony DR-Z7 from 1978, slaughters them in almost every conceivable way. These are not $700 headphones by any means. A good way to think of the MDR-Z7 is like the spoiled grandchild of a millionaire: it may seem like it has everything going for it on the surface, but in reality it lacks all of the skill and talent that got its family it's riches in the first place.
Perhaps I'm being a perfectionist, but these headphones did not satisfy me at all and didn't come anywhere close to besting my own equipment, most of which is over 30 years older than it and wasn't nearly this expensive when it was new. That is what I would call a problem.
Peace.