Pros: Great tonal balance, imaging and isolation
Cons: Inefficient, slight bass emphasis, very long break-in required
Tonal accuracy is very good. I am using as a reference my home theater with Sunfire XT ribbon hybrids and Bag End professional mastering subwoofers. The all important mid-high region is spot on. Bass is slightly emphasized, true, but the degree is exaggerated IMO.
Transients are very good, bordering on excellent.
Imaging is very good, bordering on excellent. Bettered by semi-open and open headphones, but they have their own drawbacks.
Comfort is very good - one can adjust the spring tension to one's preference - very nice feature.
Isolation is Good to Very Good - a bit above mid-pack. I haven't seen a variation in this aspect amongst closed backs, excluding super high isolation special purpose cans.
Main drawback is load/efficiency. In my experience these can not be adequately be driven by either a laptop sound card or by an MP3 player, even the powerhouse Cowon D2. I have a Turtle Beach USB DAC/amp at work, and a Total Airhead for travel. Without amplification, sound suffers substantially.
Note that if you are listening to these without a few hundred hours use on the phones, you aren't getting the full sound quality. Over time, I found that the bass became less prominent, mids/highs smoother, and imaging improved substantially. These phones have one of the longest break-in periods of any audio product I have ever owned.
I can and do listen to these all day long at work and on the plane. Very non-fatiguing, highly recommended.