I had a brief listen to these couple of days ago. Here are my impressions:
First of all I didn't find the trebles harsh at all, unlike what many others reported and I'm actually very sensitive to trebles and prefer usually a slightly darker sound. What impressed me immediately was the exceptionally good timing and dynamism of the rhythmic foundation on Michael Jackson's Dangerous (excellent record from recording engineer Bruce Swedien btw.) . The bass drum, the snare, the hi-hats sounded as one full body with exciting transient response. But they sound kind of very very stiff if that's the right word to describe it. It wasn't a laid-back experience. No closing your eyes and diving into a sound space where you lose yourself... I'm sorry but no...
I was also surprised that they have a very thick lower midrange since I was expecting a more treble-heavy sound character due to others' listening experiences and I was very happy that the trebles were well balanced against the bottom-end and they were also silky. But for me the lower midrange was basically the reason that prevented me from considering them as my next purchase. The 150-300 Hz region seems to overshadow a bit the rest of the tonal balance but fortunately without having any negative effect on resolution. They have fair amount of resolution but still I wouldn't count resolution as one of their biggest strengths. For those who are familiar with the little brother of these (Panasonic RP-HD10) I think the Panasonic has better resolution than these.
Another disappointment for me was the soundstage. Although instrument separation is very good, the soundstage is, I think, not big enough for a headphone in this price range. But in return you get a very impactful rhythmic foundation.
To summarize:
Soundstage: Somehow close in but impactful. Don't expect a three-dimensional space like you would get on the HP-DX1000
Tonal character: Low-midrange-heavy but higher frequencies are not veiled either. They don't have a natural tonal balance in my opinion, which is fine for a hi-fi headphone but I didn't really like the tonal character they create. It's somehow too stiff, cold and unnaturally exciting. Also the lowest frequencies weren't really that present which was another bad surprise.
Build quality and looks: Perfection here... They are probably the best looking headphones I've ever seen. But they are heavy, they are REALLY heavy!
As you can see, my first opinion is not very positive and I'm sure that due to the restricted listening experience I may have misjudged them in some aspects but still I don't have the feeling that I will one day fall in love with these headphones. Which is very upsetting for me, since, as a more or less Panasonic fan boy, I was really looking forward to the Technics comeback...
After couple of songs on these I switched to the CD900ST and god it felt so good...