Pros: Excellent mids, beautiful timbre, warm signature, deep soundstage, comfort...etc
Cons: Non to my knowledge
The HD600 is one of the best headphones around. They are neutral, easy to drive, comfy, with a touch of warmth and enticing natural presentation and timbre. I didn't like them the first time I bought them with the stock cable. I bought another pair driven by the formidable Beta 22 amplifier and the HD600 was transformed into another league.
Although I listen mostly to my K702 which is more accurate in comparison to HD600 warmer tone (which is closer to concert hall sound IMO) I save the HD600 for very special listening sessions, I don't use them for occasional listening at all but only when I really need to enjoy rather than analyze my music.
The highs are soft, smooth, non fatiguing. The mids are large and wide and the bass is just right, without being exaggerated. The sound stage is not very large like the K702 but the instruments and the performers are very close in very good distributed space which gives a very intimate musical experience.
The greatest thing about the HD600 is the easy amplification. A uDAC can drive them to very acceptable level and they can excel with most available amplifiers with a neutral sound signature
Some reviewers believe that the HD600 is boring. I think this can be attributed to several factors, poor synergy with amp and source, stock cable, lack of burn in or may be personal taste!
IMO the HD600 is the best headphones under $300 (unless you find the HD650 for less than 300!), and may be the only headphones you will ever need if you keep to one HP.