Pros:extreme faithfulness to the sound
Cons:don't know, still looking for one
The Bottom Line: If you're obsessed with the "real sound", with hearing what's on the wire with no modifications whatsoever, look no further.
I don't care about "pleasant" sound, i want to hear exactly what's "on the wire". I'm a dyed-in-the-wool audiophile and i'm also playing electronic music. So, the precision of the reproduction is paramount to me.
Recommend this product?
Well, the HD600 are excellent in the field of accuracy. What you hear is really what's on the wire. The sound is transparent and has an "airy" or "light" quality (someone said: "it's like they were designed by an elf engineer from Tolkien's books").
Some people claim that these phones don't have enough bass. Actually, the bass is there, it's just not exagerated like many cheap phones do - again, you hear exactly what's on the wire, no more, no less.
So far, they're the most comfortable phones i ever had. I could wear them for hours with no problems. Also, the sound is gentle so your ears don't get tired.
After comparing them to my other high-end phones (a pair of Grado's), i came to the conclusion that Grado actually boost the high frequencies a little bit, therefore making the sound bright. I know this is contested by some people (which say the Grado's are "revealing" not "bright"), but to me it's obvious, after comparing the two for months in a row, and comparing both to my Alesis studio monitors, that the Sennheiser's are flat while the Grado's pump up the highs a little bit. Also, i've seen frequency response graphs on headphone.com which confirm my view.
Anyway, IMO the Sennheiser HD600 are, among the phones i tried so far, the closest to a perfectly unadulterated reproduction of the sound. Too bad that now Sennheiser released the HD650 so i can't claim anymore that i got the top-of-the-line model. :-)
The wires are a bit flimsy, but they are replaceable.