My pair, which recently arrived, started out with loose bass and rough mids and treble, and have settled with tighter bass and smoothed out elsewhere. This happened very quickly, within 24 hours of use.
What's surprising for me is that, unlike the HF-1, which had a treble that was annoying with anything other than a fairly expensive amp, the HF-2 are more forgiving, sounding reasonable even out of an iPod, more so even than an ESW10JPN IMO. Now I understand why some people have even downgraded their amp when using them because a big, beefy amp isn't necessary for them.
I am a bit disappointed about some dents in one of the cups on mine, as well as the "Head-F1", but good sound is more important ultimately.