Pros: Fast, low/high extension is good, detailed, comfortable, light, well isolated, shortcomings can be well overcome by equalizing
Cons: Benefits from an amp (although marketed as easy to drive), sometimes artificially sharp or 'nasal', deeper bass lacks impact
Every time I put these headphones on I have to get used to some little nuances. That's because with some records, the mid-highs sound ever so slightly more hissy than with my Audioengine A2 look-a-likes, and my subwoofer is way more muddy and loud than the articulate, accurate bass of the AKG K 272 HD. The initial impression wears off after the first few minutes, from which onwards I really start liking the sound of these cans.
[EDIT: I confess, I didn't want to write this because I thought all the hi-fi people in here would flip at me but honestly, with equalizing by +3dB at 20-80Hz region and a -2dB at 14kHz onwards or by just putting the bass boost to level 2 from FiiO E7, the sound is much more pleasant and warm from these cans, while retaining their accuracy and fast nature. I don't perceive any negative effects after equalizing, they still remain accurate and fast.]
AKG K 272 HD shines with Benassi Bass and other raw sounding effects in music, which might be a partial reason why I like chiptunes and dubstep nowadays so much. There isn't much to say about vocals with these cans, they sound good but not exceptional. Some very nasal female singers sound really hissy, since the cans give them a boost of their own due to the mid-high fuzzyness (which might just aswell be the general sound-signature of neutral headphones, don't know. Anyway it goes away with the equalizing). With orchestral music and soundtracks the mid-high fuzzyness makes the track sound a bit noisy or sterile, but the bass boost setting in the FiiO E7 compensates that well when set to level 2. I've read the sound stage on these isn't too good, but at least in games I found them really good at pointing out enemy locations based on footstep whether they came from above, below, or somewhere else.
They're a tad sterile and nasal without EQ, but with it they're absolutely terrific. I was considering getting a crapton of other cans while these weren't satisfactory, but to me these are just perfect when I get rid of the excess sharpness.