Pros: Extremely comfortable; great "symphonic" sound; detachable cord; works surprisingly well with MP3 players
Cons: Does not silence outside noise; sharp kicky bass overwhelms the drivers at high volume
Sennheiser has a reputation for excellent headphones all the way from the ultra-tweak audiophile market to mass-market budget buyers. The HD-570, at around a hundred dollars, is at the very top of what most would call "mass market".
THE GOOD - COMFORT
The most outstanding feature of these headphones is their comfort. They are very lightweight, with soft open-cell foam surrounds covered in a velour-like cloth. You can literally forget you have them on after a little while, at least until the cord touches. I have never found headphones that are as comfortable as these.
THE GOOD - FEATURES
The HD570's have a very nice touch. The lightweight cord (which is nice and long, something like 3 meters) detaches from the headset. What this means is that if you get tangled in the cord, it just pulls out, without damage. As most regular users of headphones know, a good hard yank on the cord can sometimes break the wires inside the headset, and that can be a real pain to repair (or get repaired for you). That will never happen with the HD570's, and given that the generous length of the cord will encourage you to walk around with your headphones on, that's a good thing.
And, if you do manage to munge your cord, you don't have to ship the headphones anywhere to get another. Just order it from Sennheiser's website.
Speaking of which. The HD570's cord has a standard 1/8" stereo jack, with an adapter for 1/4" stereo jacks. All connectors and adapters are gold-plated for a clean signal.
THE GOOD - SOUND
Sennheiser has built their name on "open air" designs for their headphones. What this means is that your ears are not enclosed by hard ear cups and pads that seal off your ears... the headphones are designed to allow air to move through the headset freely to your ears. The HD570's are a prime example of this.
This affects sound in several ways. The most obvious is that sound from the outside world can still get in, so if you're looking for "isolation" headphones, this isn't them. It also means that bass response for heavy, punchy bass is not equal to a "sealed" system, as the high pressure pulses can partially dissipate through the foam around your ear. More on that later. However, it also prevents the bass response from being artificially "boomy". For some types of music, in which the bass is sustained (classical, vocals, progressive rock, jazz), this is ideal. Also, because there is not a fixed-volume air chamber, there are no frequencies (high, low, or in-between) that will sound artificially heavy or light (no "standing waves" or resonances).
The HD570's, therefore, have a wonderfully flat response over almost the entire audible range.
The last benefit I've noticed with these headphones, which I attribute to the efficient "open air" design, is that it doesn't take a lot of power to make them sound good. Plugged into my iPod Shuffle (which is dwarfed by the full-sized headset), I can still get all the volume I want. Yes, I have to turn it up more than I would for earbuds, but not to the point of distortion.
THE NOT-SO-GOOD - PUNCHY BASS
As mentioned above, the "open air" design does not isolate your ear in a sealed chamber. This means that quick-attack thumpy bass (as found in action movies, heavy metal, and some electronic dance styles) suffers. There are those who would argue that the HD570's are giving you exactly what is being fed to them, but if you're expecting more bass, you're not going to be happy. Since happiness is the difference between expectations and reality, if you're expecting slammin' bass to shake your skull... no. These headphones, while capable of being quite loud, won't do that.
In fact, it's possible to overdrive the HD570's to the point of crackly breakup. It takes a lot of sharp bass to do that, but it's possible.
THE NOT-SO-GOOD (MAYBE) - SOUND ISOLATION
As mentioned earlier, you can still hear the outside world due to the "open air" design". If you're trying to shut out annoying sounds with your headphones, these ain't the ones. If it doesn't matter, or you want to be able to hear outside (keeping an ear on your kids, walking and wanting to hear cars), you're just fine here.
For folks who mostly listen to music that doesn't kick and scratch, these are wonderful headphones. Comfortable, rugged, with nice ease-of-ownership features, with sound quality easily equals or exceeds the competition in the price class, the HD570's are everything that most people with a hundred dollar bill burning a hole in their pocket could want. Just be sure that your mission profile matches what the HD570's are best at.
After buying a pair for myself, I bought more for friends as gifts. That's my ultimate compliment.