Compared with all of the other headphones I have been going through these are by far the best, leaning slightly more toward bass, though still maintaining crisp treble due to the dual element design. I have not noticed any significant changes over the hours I have used them, burn in time seems to be non existent. The stereo separation is average, and they sound like they are half way to open air headphones. Sometimes the bass definition is too much, as it makes some mid bass sound bad (the beat in Glamorous, by Fergie for example, can sound less deep) I have tried them on a micro stereo (gpx brand) my mp4 watch, and a PC, The headphones sound as good as what you plug them in to. The comfort is good, they just take a while to find the right ear clip size and height. Another great comfort feature they have is the rubberized surface that is present wherever they touch your ears. The part that goes in your ear often comes out greasy, but it easily wipes off. I have received lots of comments on how unique these look, and none of them where bad, mostly admiring.
I chose these ($150 Koss KDE250) over:
(headphones I have tried and returned)
$45 ZaggPhones
$70 Audio Technica ATH-AD700 (open air)
$35 Koss PortaPro
$145 Etymotic Hf5
$80 Koss CC_01