So I got these things yesterday around noon... I've listened to them for about 6 hours or so since. Last night a spent some time putting them head to head against the HF-1 for some fun (didn't compare them to the MS-1, it wouldn't even be fair). For the record... I don't believe in burn-in. Based on the reviews I've seen, my pair sits right in there as far as sound goes on "burned in" cans.
First off... these things are a ton heavier than the HF-1s. The cord is shorter (maybe a foot) and the cord is very stiff. They are not uncomfortable other than the cord doesn't cooperate yet

. They feel very solid in the hands and on the head.
Sound wise, they are amazing.
Bass: The bass on these things is incredible. I heard (felt?) foot stomping on live acoustic recordings I only hear with a big sub. They go lower than the HF-1 and the bass is stronger overall without being overpowering. It's just there in force. Kick drums are super punchy, bass notes are easy to distinguish, and you can hear the LOW stand-up bass notes the HF-1 seems to ignore.
Highs: The highs on these sound perfect to me. When switching between the two, the HF-1 has a very sizzly super high frequency range (I have abnormally sensitive high frequency hearing up to the 23khz range... I hear like a 5 year old). The HF-1 seems to have a big push in that range so certain instruments or samples sizzle (not quite sibilance, higher frequency). The HF2 does not. The sound is still there, but it sounds far more natural. To be honest, I never noticed the problem in the HF-1 since it's so common in loudspeakers and headphones alike.
Mids: The two are very close in this area. They're Grados. Voices on the HF2 sound a little more natural, but It sounds more like it's related to the sizzle of the highs (read ssss's). Acoustic string instruments like mandolins, guitars, violins, etc. sound very close between the two.
Other: Instrument separation is definitely better on the HF2 and the soundstage is a little wider (although still mostly in my head). Everything just seems to sound more like it should.
Definitely fantastic headphones. My co-workers were making fun of my expensive purchase, until I put them on my bosses head.