Pros: Luxurious midrange, full and extended bass, smooth treble, comfortable.
Cons: Maybe a bit too full-sounding? Not quite as resolving/detailed as some of its peers.
Let me just say one thing up front: if you have any complaints about the speed or the bass extension of these headphones, you need a better headphone amp. /endofdiscussion The HD600s will take the best in source material and amplification, and give you the best sound in return. It's not coincidental that these cans are held up as the reference's reference: more than any other headphone I can think of they sound like whatever it is you are listening to. Their most notable audio characteristic is this ... amiable compatibility. That and the ability to play cleanly at very loud peak levels. Combined, the HD600s are ready for whatever you care to throw at them, never drawing unwanted attention to themselves, always sounding great.
Perhaps part of the secret to this neutrality and high enjoyment factor is the way they dial down the resolution just a tad. A fraction de-focused, one notch less treble intensity - blending the music into a coherent experience rather than individual strands of detail. Some people might disapprove, I call it genius.
These are comfortable, durable headphones built to a high standard. The foam pads on the earcups and headband died after a decade or so, but I easily replaced them with the new parts from Sennheiser.