I have ATH-M50s that I use at work and those were the first real cans that I ever owned. I then bought the HE-400 for use at home and I really enjoy listening to music on those. As others as have said the treble can be a bit harsh and I have noticed this as well compared to the M50. That is the only real downside I have noticed so far. However I do find myself just sitting in my desk chair and enjoying the music from my HE400. I did EQ them a bit to tone down the treble (6k-10k) range and they sound great. I listen to rock (classic, alt, indie) and R&B and they do well.
I have my HE400 being driving by the Schiit Magni/Modi stack.