Just got them, very early impressions.
Don't like the balanced pads - it makes the bass too wide and uncontrolled (at least with my FiiO E10K), and overall it doesn't seem to have the clear (treble-prominent) sound I want (if the treble is tamed, it doesn't sound "real" to me unless the recording is extremely good). I literally only listened with those pads for less than 10 minutes, so I could be off about the lack of clarity (I'm not off about the bass, though [to my ears]).
Switched to analytical (pretty easy to do once you read the instructions and just trust that the notch will work as you turn the pads), and this is more like what I expected.
There is definitely something like a hard edge in the treble. Sibilance is exaggerated, yes, not neutral - usually it is merely noticeable, instead of irritating, and most of the music I like doesn't have vocals, anyway.
Bass is significantly more focused than with the balanced pads, but there is (usually) enough bass for me, and it still goes into sub-bass territory that many other open headphones don't reach.
These headphones do texture, timbre, and detail very well. Obvious improvement over the ATH-M50x and DT-770 80 Ohm, and perhaps over everything else I own (see my first post in this thread for a list of most of my other headphones).
Instrument separation during busy passages (lack of congestion) is definitely an improvement over the DT-770.
Impact is good - drums kick when they should, etc.
With many recordings, there does seem to be a weird gap somewhere in the treble that reminds me of the AKG K701. Looking at graphs where the two headphones match up a bit, it may be in the 4-5.x KHz range? Maybe it sounds "missing" due to both headphones' uptick from ~6-10 KHz, since the DT-1990 doesn't share the K701's 2-3 KHz peak, but they both have this obvious (to my ears) hole in their response?
After a bit more listening, the treble can be a bit too harsh. Will try the balanced pads again. I've written enough, I think.