Ultrasone fan here. I have an Ed.8 and looking forward to buy the forthcoming Ed.10. While waiting, I thought I should give 2900 a try.
Although the sound is not as refined compared to Ed.8, it's a headphone capable of digging a lot of detail from a recording, while managing to keep the sound much more enjoyable than, let's say, a K701. The bass performance is excellent (but maybe not as good as Ed.8 which is a closed design after all), tight, controlled, punchy, the mids slightly recessed, the treble a little on the bright side as every Ultrasone (the burn in helps a lot but not to the point of smoothing it completely). The soundstage is right, neither huge and detracting from the enjoyment of a rock tune as some "audiophile" headphones, nor completely absent as most Grados etc. I wouldn't say the soundstage has much to do with the open design (you can obstruct the back without much of a change in sound), but rather with the latest S-Logic algorithm, which seems to provide a better, more realistic sense of space compared to my Ed.8.
It's a fair and fairly priced headphone, offering, in my opinion, excellent value for the money. A must try for the Ultrasone fan, a good alternative to the Grado's, Sennheiser's and Denon's in the price range (and in my opinion better than most).