OK, now that I've had more time with my new M-80s I'll give a more thorough impression:
Previously I complained about the (for me) relatively low clamping force because I have a smallish head. I took them to class for the first time today and had no problems with them moving around on my head or any fear that they would fall off while I was walking. At this point, I have to say that the light clamping force actually makes the M-80s comfortable in a heavenly way, so I'm willing to take a little bit of possible movement for that level of comfort. The left earcup deal remains, however. The left ear is noticeably in more discomfort after use than the right, and it is clearly because the left earcup does not tilt as much to conform to the angle of the ear. I suppose playing with the headband could allow one to have both earcups at the same angle. It's not that the left ear is in a lot of pain, it's just that after use (today, 1.5 hours) the right ear feels perfectly normal while the left ear is somewhat fatigued. If I could manage to angle the left earcup so that that no longer happens, the M-80s would honestly be more comfortable than my KRK KNS 8400s, which are very comfortable circumaurals, and I'm saying that as someone who used to be a supra-aural hater.
The sound is just great. It's both balanced and fun. My 8400s bring out a little more detail than the M-80s in classical music, but the 8400s have harsh highs where the M-80s don't. Listening to dubstep, my 8400s have tight bass but lack in impact while my M-80s manage to have both tight bass and impact. The mids bring vocals out quite well. I'm still not an audiophile when it comes to my listening abilities, but I can say that the M-80s sound balanced and fun at the same time.
As far as complaints, the M-80s leak quite a bit for me. I tested them by playing a song at normal listening volume and holding the cups together in my hands and in a quiet environment you can hear the music from about 8 feet away. I feel like if I was doing work in my favorite study spot (not a library but is just as quiet as one) with my M-80s I would definitely turn the volume down a little bit as to not disturb anyone nearby. I closed up the vents with my fingers and the leaking decreased a good amount, so I guess that's just a factor of the design. As to isolation, they actually isolate a lot better than I thought they would. Not quite as well as my 8400s, but surprisingly well for semi-open supra-aurals. At the same volume my 8400s would make it that you can't hear a conversation near you at all my M-80s would make it that you can barely hear unintelligible sounds. Overall I think the isolation is perfect for a portable headphone (in terms of some degree of outside sound being necessary for safety). Also, wind noise is definitely a problem. Had a little bit of wind while I was walking and you can definitely hear it.
Ultimately, I completely recommend M-80s. The build quality and look are fantastic. The extras are great. The sound is great. The comfort is great. It has only a few minor hiccups, but they are certainly beat out by the positives. Probably some of the best value portables out there.
