It is spikier or rougher than a number of other cans. It has a prominent treble spike which has been measured and I agree with my listening. The treble spike doesn't seem to bother on some recordings but on plenty of ones with cymbal work or noises during movies where glass breaks for example its quite etched/sharp.
The HD600 is smoother, so is the HE500 and Alpha Dog.
However it also has a somewhat elevated bass response, pretty strong compared to many purely audiophile cans but not nearly as powerful as many bassheads cans. The mids a somewhat recessed if you compare to cans like the HD600, HE500, LCD models or even Alpha Dog and JVC DX1000 - but not massively so. The only offending dip in the response as I've said in the past is a dip somewhere in the lower midrange that makes them sound dry and thin to my ears with some vocals, guitars, basses.
I too had that same "dry and thin" impression of the 600's back when I first got them, but coming from a more lush rich intimate headphone with a mid emphasis (LCD-2) it's more or less your ears adjusting to the sound, the TH600's are a little cold when compared to headphones like the HD600/HE500/LCD (the ortho sound in general is rather intimate with a mid emphasis). I can say now with full confidence that the TH600's aren't cold, and rather flat through the mid range, not recessed.
There is that spike though, that sadly doesn't exist in the TH900's, which is the only reason why I still have a nagging temptation to upgrade :D I have made a slight work around using tube rolling on my Pan Am to compensate for the treble spike, and even with the worst gone I do hear that cutting edge treble from time to time. If this is a deal breaker, I would say search for a different set of cans, perhaps the TH900's.