Pros: good isolation, substantial bass, pretty balanced sound
Cons: tight clamping, feeling of pressure that closed cans create
the m50 was released a few years ago by audio technica as the flagship of their "m" studio monitor line.
and, like all audio technicas, it is colored in one way or another.
this particular headphone definitely has more bass than a strictly neutral set of cans should. but, the bass is quite impressive for a phone of this caliber and price range. using the "heartbeat" test track from the "Open Your Ears" headphone test album, the m50 produces more low frequency rumble than any headhpones i own or have heard. (bear in mind i have not heard denons or ultrasones).
the general sound is warm. the headphones are colored forward in the mids such that the bass does not step on them too much. this creates a fairly engaging sound signature. the highs are recessed just a tad, fortunately, because they are just a tad grainy as well.
the imaging and soundstage are pretty respectable for closed cans. but, the soundstage doesn't really "take off" until they are amped and turned up pretty loud.
when listening to these extensively, you get used to the presentation, and the one drawback that reamins is the mid-bass is just a tad unresolving. i wouldn't go so far as to call the mid-bass "sloppy", but it doesn't have the attack and decay of higher end headphones.
overall, the m50 performs very well for a headphone that you can buy for around $100.
it's biggest drawbacks really don't come so much in the form of sound quality as they do in the region of comfort. As the clamping force is a bit much, and prevents me from wearing them longer than a couple hours at a time.
Also, as a result of them being closed cans with a tight seal, your ears will require quite a bit of adjustment when putting these on. after a few minutes, the pressure will equalize, but at first it feels like your ears need to pop.
as for audio quality. i struggled between giving these 3.5 stars and 4 stars. but, i have to be honest here. if 3.5 stars is "very good" and 4 stars is "excellent", then 3.5 stars it must be. they sound very good to my ears.
edit: after a couple months constant use, it seems to my ears that the midrange took a backseat after burn-in. i'm not certain whether burn-in is real or placebo, but either way, the mids on the m50 afer a few hundred hours use are now somewhat recessed, possibly even slightly veiled. not too objectionable, but noticeable.