Mixed Feelings

General Experience
I have to admit that I have mixed feelings about these headphones. At first I really loved them, but I'm starting to develop more of a love-hate relationship with them.

Comfort
Maybe more important than sound quality is comfort. If you can't stand to wear the headphones, then you won't enjoy listening to them, even if they have golden sound. There are two aspects to comfort that I consider important. The physical comfort, and a harder to describe sensation of 'fatigue'.

These are very comfortable to wear. I can wear them for hours without discomfort. Many headphones irritate my ears with their scratchy pads. These are soft and well cushioned. They also don't cause my ears to sweat, like some do.

Then there's the fatigue aspect. Maybe you know what I'm talking about. If not, then it's hard to explain. Some headphones just make me feel tired after listening for a short time. Maybe it's the sound quality, maybe it's the discomfort, but some make me just want to stop listening to music altogether as if it's a chore. These don't give me that feeling.

Noise Cancellation
I assume that the reason that you're considering these is for their noise cancellation feature. The noise cancellation is just OK. Many pro reviews that I found said that it was as good as the Bose systems. I got an opportunity to compare them myself once at an airport. It wasn't true, nowhere near as good. That said, it will quiet the cooling fans in your office. For flying I've come to prefer canalphones (passive noise cancellation, just plug your ears!) In my opinion, these are NOT good for use when flying -- they don't cancel much and they're a pain to use when flying (more on this later). The battery life is good, though I sometimes forget to turn them off so I've never really found out their real lifespan -- I always kill the batteries before they die naturally.

All noise cancellation headphones make a hissing noise when in use -- with these it's barely perceptible -- you have to try to hear it during silent passages. In that sense, they're good for music with quiet passages (like Classical).

Sound Quality
All of my comments on sound quality apply to when the noise cancellation feature is turned on. You CAN use them without the noise cancellation feature, but the sound is a mere shadow of what it should be, muffled, with poor frequency response, and little detail. If the batteries have died, I don't use them.

Frequency Response
These headphones have a good balance across all frequencies. The high frequencies are very clear though some people may find them to be a little bit light on the bass. Bass is there, but it may be too subtle for some.

One thing that separates the best speakers/headphones from the 'also-ran' competitor is their ability to pleasantly and evenly reproduce all frequencies even at low listening levels. Many speakers do well when driven hard, but become muffled and it becomes difficult to distinguish individual instruments/notes at lower volumes. I've found that with these I can listen at a VERY low level and still pick out even the most subtle parts of the music. This is especially important with the noise cancellation feature because you find yourself enjoying the quiet -- if you're going to play it LOUD, why not save your money and just buy a good set of studio headphones and drown out the background noise?

Distortion
Unless you're into playing your music REALLY loud they don't distort.

Dynamic Range
As I write this, I'm playing Hayden's Symphony #94 - Andante ("Surprise"). It varies greatly from the quietest to the loudest passages. These headphones can easily accommodate the entire dynamic range of the digital sound files that I'm using from the faintest whisper to loud enough to bother my ears, yet I can still hear every detail. I have never listened to this recording before -- there is some coughing in the background -- I actually just took of the headphones to see if it was one of my coworkers or in the music. Then a passage that got soooo very quiet that it was quieter than a whisper followed by the 'surprise' that was so loud that I jumped and nearly tore them off of my head! Problem is that they're so accurate that I can hear far too much background noise (shuffling pages of the program, people in the audience moving around, sniffling, footsteps, etc) in addition to the music!

Usage Recommendations
I listen to all different genre of music. I have a tendency to switch headphones based on the type of music that I'll be listening to or the listening environment. These are best for use in the office where I like to drown out background noises without having to turn it up too loud. I'd recommend them for Classical, Jazz, Light Rock, Country, Pop, Vocals, Big Band. I don't recommend them for Rap, Metal, other heavy driving styles of music.

Reality Check
Wow, with such a glowing review, what could be better? Er, um, well, there's that hate part of the relationship.

These are NOT good portable headphones (thus my comment about not flying with them). In fact, they're not even that great when tied to a portable device when sitting still. The cord tangles easily and gets all wound around itself. I frequently untangle it, but just hours later it's tangled again. The battery pack and electronics for the noise cancellation feature are on a dongle half way through the cord. If you move too far it gets pulled off of your desk and pulls your CD/MP3 player off with it. When walking around you end up with this large dongle hanging out of your pocket, and even with the swiveling clip it's hard to clip anywhere out of the way. They also don't fold very easily. They do fold down quite flat, but it takes so long that I just don't bother. They stay at my desk and never go anywhere.

Overall Conclusions
If you're looking for a set of headphones to use at the office to silence office background noise (A/C compressors, computer fans, printers, but NOT chatter or talking) then these are great, though you might find that you're better off with a good set of sound isolating studio monitor headphones -- if you don't have problems with sweaty ears.

If you're intending to fly with these headphones, consider the Boss headphones if you can afford them, or a much cheaper set of canalphones if you're on a budget.