Pros: Bass, Comfort, Looks, Bass
Let me start off by saying that I purchased my TH-900s from an authorized dealer for $1,300 brand new (which I still feel is a bit above their true value) about one month ago. I have owned (and sold) several pairs of D7000s already, so after reading many reviews claiming the TH900 to be an upgrade over the D7Ks in pretty much every way I decided to buy a pair. My first impression was that they sounded very similar, but there are actually some serious differences. It's worth noting that I went into this situation with a bit of bias. I really, really expected to love the Th-900s.
These are without a doubt the nicest looking pair of headphones (well, in my opinion) that I have EVER seen. The cups are just absolutely beautiful. The pads are a total improvement over the old D7K pads (softer, deeper, they even look a bit nicer). The cable I consider to be a bit of an issue (just like the D7Ks). It's non-detachable and 10ft long, terminated in a 1/4" plug. The wooden stand they ship with these is a nice thought, but kind of a waste if you ask me. It looks and feels cheap, I would have rather had a nice storage box (the one included with the Th-900s isn't quite as nice as the one that came with the old Denon line).
Bass: Bass on the TH-900s is a bit more extended than the D7Ks, but lacks the overall impact of the D7Ks due to it's lack of overall weight. Bass is clean, crisp and well defined with the Th-900s, however it's only a slight improvement on the Denons. Some people may prefer the overall weight/impact of the D7Ks bass to the Th-900s slightly better defined bass.
Treble: I have occasionally been bothered by the agressive treble presentation of the D7Ks. I sometimes find it a bit too harsh or sharp sounding to my ears, not always but occasionally it bothers me. The Th-900s improve upon the D7K's treble presentation in every single way. It is detailed, crisp and possibly the best I have heard from any headphone to date.
Mids: This is where the Th-900s lost me, and where the D7Ks proved to be my preference. The mids on the D7Ks are slightly recessed. I was expecting somewhat of an improvement on the TH-900s. Well, it turns out that it's quite the opposite. The TH-900s have an even more recessed midrange than the D7Ks do, vocals can sound a bit distant, muffled and just bad overall (well, at least for a headphone in this price range). This makes the TH-900s sound a bit strange to me, their overall presentation just doesn't sound natural in any way. The D7Ks do have a typical V-shaped sound signature, but it works well for them as they are still decently balanced overall. I feel like every aspect of the sound compliments another and they sound truly euphonic. The Th-900s do make some improvements on the D7Ks, but aren't as enjoyable of a listen overall.
The pricing concerns me a bit too. I feel like these would be an appropriate follow up to the D7Ks at a similar price (<$1000) but are outdone by quite a few options well below their current asking price. I purchased mine at $1,300 (USD) and I don't feel like they're worth that. If I were a buyer who purchased a pair at the original price of $2,000 I would feel a bit betrayed or misled after seeing the recent price drop.
Overall these are a pretty good sounding pair of headphones but not worth their asking price in my opinion, especially considering all of the other options.