Received the HM5s recently and am so far impressed. I bought them for an office headphone (where isolation is key) to replace Ultrasone HFi 580s, which I find just way too harsh to listen to for more than 15 minutes. First impression was that the sound was not nearly as aggressive or exciting as the Ultrasones, which is exactly what I was after. Initially detail retrieval seemed worse than the Ultrasones, but it quickly became apparent it was just that the HM5s don't have such exaggerated, piercing treble. After more listening time I'd say detail retrieval is quite a bit superior to the Ultasones, in fact probably on par with the W1000x I have at home, although the HM5 loses in dynamics and soundstage in that comparison.
I noticed that while isolation is generally quite good, they do let in a certain frequency, similar to if you cup your hands over your ears. I opened up the 'phones and would take a guess that is due to the backs being absolutely cavernous with just some felt damping on the back, so a sort of cave effect occurs. I've stuck some dynamat inside the back and put in a little bit of cotton wool as well, and it seems to help a bit but not solve the problem completely.
Overall a decent, neutral sounding headphone. Definitely a relief to hear mids again after the Ultrasones
