Out of box impressions: These cans come in a cheesy $10 Coby-esque plastic blister pack - AT doesn't seem to be so hot on the entire marketing thing . No matter - the headphones themselves are well-built, albeit a little plasticky. The headband is nicely padded with good quality pleather, and the construction is solid overall. The earcups are padded with slightly lower quality, but still plenty durable pleather. The overall look of the headphones is somewhat industrial, and typical for studio headphones - all black, big, and beefy. Only major nitpick is that since the cable is single-sided into the left cup, the wires to each side run externally through the partial headband, leaving part of them exposed. These exposed wires look like they might easily get caught on something and get totally jacked, but they are tougher than they look. The main headphone cable itself is fairly substantial (think Grado), and is terminated into a 1/8" end. It comes with a good quality threaded 1/8"->1/4" adapter.
Comfort and isolation: These are, by every measure, very comfortable cans. Even for my largish head, there was none of the Clamp of Death (TM) effect of my previous HD280 Pros, but at the same time, they were never in danger of slipping off of my ears, even with vigorous physical activity (headbanging included). It is impossible to not get a good seal - put 'em on, and you're good to go. The earcups fit nicely around my largish ears, and according to my better half, also around her somewhat better ears. They are not particularly heavy, especially for their physical size, and seem to be padded in all the right places. I easily wear these all day without discomfort. In terms of isolation, they are somewhat inferior to the HD280 Pros. The M30s block higher frequency background noise very effectively, but lower- and middle-pitched roar isn't attenuated quite as well. However, they isolate well enough - certainly miles better than the PX200s, and quite a bit more effective than the seals of the HD212 Pro and Sony V6/7502.
Sound: For 50 bones, I didn't expect much, especially for sealed cans. But boy ... I was in for a surprise. While not stupendously accurate, these cans present a laid back, non-fatiguing sound with a remarkable lack of that resonance and honkiness so many sealed headphones tend to display. Straight out of my Audiophile 192, the bass doesn't go particularly deep, but there is a hump in the upper bass that, at least superficially, masks the lack of depth. Thankfully, even with this non-linear response, bass notes don't sound bloated or nondescript - just punchier and more impactful. Mids are slightly recessed, but I'd stop short of calling them nasal. They are not excessively attenuated, and blend well with the smooth and fairly uncolored highs. In terms of detail, DT880's they ain't. These cans sound like they're built for the listen-while-working crowd, and make even poor recordings sound pleasant. Even with this smoothness, they certainly don't sound veiled, thanks to the neutral highs. All in all, on the warm side of neutral, with no glaring deficiencies or strengths. A very pleasing overall sound.
Ease of driving: These cans don't really need an amp - portables of almost any kind can drive them with ease. If you happen to have an amp handy, though, plug 'em in and you will be rewarded with a significantly smoother bass response and increased midrange detail. Don't buy an amp just for the M30s, though.
Comparison to other similar headphones:: To my ears, the M30s compare quite favorably to the more expensive HD280 Pros. While the HD280s are praised for their lack of mid-honkiness, the M30s have even less of it. I found the HD280s to be far too thin in the bass, and quite shrill in the upper mids and highs. Perhaps they resolve slightly more detail than the M30s, but the M30s are a far more balanced headphone, and much more enjoyable to listen to overall. I find the M30 to also be preferable to the Sony V6/7502; while the bass qualities of the two cans are similar, the M30's mids and highs are far, far sweeter and less grating than that of the V6/7502. The HD212 Pros sound like a caricature of the M30s, strangely enough. They sound as if you took the midbass hump of the M30 and multiplied it many times over, and similarly, recessed the mids much further. Females vocals I would stop short of calling 'nasal' on the M30 are most decidedly nose-holdingly wheezy on the HD212 Pros. I think that the most comparable-sounding headphone to the M30 is, unexpectedly, the open-backed PX100s. The overall tonality is strikingly similar, with the PX100s exhibiting moderately more upper bass, and slightly more open-sounding mids (not surprisingly). PX100 fans looking for some closed cans will undoubtedly like the M30.
Overall: If you're looking for some decent sealed cans on a budget, you owe it to yourself to try the ATH-M30, especially if you're looking for a secondary set for chilling with some tunes while working or otherwise kicking back. They certainly won't raise goosebumps, but they'll take good care of your ears and your wallet.