I've been listening to them for the last couple hours and my first impressions are very, very good. I haven't installed a low-pass filter yet so I'm still using a simple slope in the foobar EQ.
The soundstage is very natural sounding. The fact that nothing touches your ears lets you forget you're wearing headphones which has it's own benefits for immersion.
These work well for just about any type of music, but they are a little more picky than regular headphones. Albums that have less instrument separation will be a bit worse off with these. I think it's mainly because with badly produced rock albums, there is no benefit of having a larger soundstage, because there isn't one to begin with.
Classical music is the strongest point, but rock is still very good. Again, it's highly album-dependent. Live music and classical does the best because of the real soundstage present in the actual performances. Depending on the mix/master, studio albums can be great.
The low-end is what's trickiest part, and there is notably less than a stock beyerdynamic dt880. The bass that's absent, though, is the sort of boomy bass that you get with any headphone. These are exceptionally clear sounding which I think helps with instrument separation. Bass can be very deep when called for.
For reflection, I was referring to the sound waves produced by the driver going away from the ear, as well as waves bouncing off the ear and returning towards the headphone. Eliminating/weakening these might be important.