These things sound great - similar to my modded HD518s (they sound exactly the same as 598s with my mod) with deeper bass, a good sound stage and solid highs, yet ever so slightly lacking mids. These have an absolutely tremendous sound stage for earbuds. 
 
The noise cancellation is OK, it can completely cancel out the sound of a car working if you're sitting in the backseat on, say, a long road trip or a carpool. Noise from a crowded bus is not quite there though. The wail of the bus is typically cancelled but the crowds around you, especially the people closest to you, manage to infiltrate your ears. This is probably as noise cancellation should be but, for lack of better words, the noise cancellation is about 70% that to Bose QuietComforts. One thing that kind of irritates me is the sound gets louder when you turn noise cancelling on which tells me that some of the NC might be a bit of a placebo. It definitely feels more "under water-y" when turned on though.
 
The battery life seems to be good. I haven't replaced the battery in the week I've owned them. Can't comment on durability just yet,
 
The battery pack has all the right built-in controls for music players like a volume wheel and a skip button next to the microphone (which sounds good in case you were wondering) if pressed twice. The noise cancellation switch cannot easily be knocked into the position it isn't it. It takes a good grip and force. The clip works for any belt look or pocket.
 
Terminates in a right angle. I've never destroyed a pair of earbuds with a connection like this so I'm glad to see it.
 
Comes with a soft touch pouch that keeps them protected and can hold my iPod Nano in it.
 
Comes with a good array or earbud tips (rubber and also a pair of Comply tips which I use).
 
TL;DR
Worth the money I paid (59 USD) but the noise cancellation could use work.

I got these on a killer bargain from Fry's late last month. After two weeks I can say that my initial impression of them has improved but, in short, you should get the 558s and do the foam tape mod instead of buying these.
 
First thing I noticed was that these clamp HARD to the top of your head if you have the right (or, I suppose, wrong) shape of head and it's extremely fatiguing and uncomfy. After two weeks of frequent wear and about 4 hours of "stretching" with pillows they have gotten significantly more comfortable and I can say that with one of the most sensitive heads around. However I will be replacing the earcups with HD 558 earcups as they have more give and, I think (don't quote me on this) they leak a bit more bass than these do which leads on to the next thing.
 
They have a bit more bass than I would like. It's very deep and sounds great with bass guitars (listen to "Life in the Fast Lane" by Eagles if you wanna hear dat bass guitar strum) but it's a bit boomy and it drowns out the mids. Vocals are quite hard to hear without a proper EQ of the mids. Listen to "Don't Stop Me Now" by Queen and you'll see what I'm talking about. Freddie's amazing tenor has no effect when wearing these without a good EQ mids boost. After messing around with an EQ these do sound much more balanced now and I like the sound.
 
As for the "closed-back" mention I made in cons - if I were to compare these to the AD500X from Audio Technica with those being a baseline 100% for openness, these would be about a 55-60% openness effect. They don't have the widest soundstage and when I'm not playing music through them I can hear my Cherry MX Green keyboard (loud) though it sounds deeper and somewhat muffled. The HD 558s are more open by design and, if you take the foam tape out of the cups they sound amazing - better than these for certain. I'm contemplating modding these cans to see if I can get a more open soundstage by doing what this guy on Reddit did. https://www.reddit.com/r/headphones/comments/2t8jtw/my_modified_sennheiser_hd518/
 
The cable is stupid and you need to use the terrible adapter to use it with most audio equipment and you can get replacements but only from Senn. Seems like a money grab to me. 
 
However, with all these negatives I listed I still like them enough to keep them for as long as possible. They were $60. Come on, hard to beat that. Would buy again but would grab a pair of HD 558 earpads on the way out.

They sound better than anything I've heard at this price point. I use these earbuds with my iPod Nano every day. The one thing that makes these things annoying as crap is the stupid cable that gets tangled and stays tangled. 
 
They isolate noise OK. My ears aren't the best shape for them so if I wiggle my ears sound suddenly leaks through. I replaced the rubber eartips with the ones from JVC Marshmallows - in my opinion the most comfy tips for buds. They make the driver a bit more distant from your ear but this is solved by raising the volume.
 
Separation is poor which is to be expected. Nothing like my HD518s and I don't expect them to be.
 
Honestly, for 6 bucks these are great. I've never owned any really great earbuds but I do know that I normally tear through earbuds because I am not nice to them and none have lasted as long as these have. I got these right before the 2014 year ran out and, seeing as it is currently September you could say that these things are build pretty well.