So now I've had a week with these headphones, and here's how they've changed for me over the past week. I've listened to these about 10 hours a day for the past week, as well as letting them burn in overnight. There were definitely moments when I strongly considered taking them back to the store, but those moments are over now.
When I first got them, the bass was loud, but not overpowering (for me anyways, as I tend to like bass more than the treble.) The bass has settled a bit and is a little more laid back than it was at the first.
The upper range was sometimes extremely harsh, and there was some pretty heavy sibilance, especially when listening to certain albums. (I remember feeling fatigue after listening to Kings of Convenience's Riot on an Empty Street album due to the excessive sibilance in every "s" they would say. It had been described as an "icepick in my ear" by someone else on the forum, and I can relate to that. The good news is that the sibilance is almost completely gone at this point. I'm listening to the same album right now as I write this, and the s's sound much more natural and normal.
All in all, I'd say this is an excellent purchase. The one thing to be wary of, however, is that these phones do have a high level of detail for a pair that costs $80. I've found myself in the last week getting frustrated with certain albums while listening to them through these phones, mainly because production quality will make a huge difference in whether the album sounds good or not. I posted earlier about Norah Jones' first album having a bit of compressor difficulties with her voice on the first track, and those are still brought out by the headphones. I'm convinced at this point it's not the headphones, but rather the mastering on the disc itself. If that kind of thing distracts you, you may be happier and more liberated without these headphones. If you like to hear every detail as clearly as you can, but you're still on a budget, I'd definitely suggest these.
Also, these headphones might not be the best to get if you're a heavy classical listener. I feel like the strength in these headphones are pop, electronic, rock and jazz. Anything with plenty of percussion will sound wonderful. The S4's naturally warm sound can make classical music sound a slight bit muffled at times, especially when listening to small ensemble music. Again, the sound signature might become more balanced over the next couple of weeks, but I'm not counting on anything at this point. That being said, I can say that upright bass in a jazz or bluegrass style music sounds excellent on these phones. Robert Plant and Alison Krause's Raising Sand sounds amazing on these, as does Jon Hopkin's Insides album.
As for comfort, I think you'd be hard pressed to find a pair that feels so comfortable in your ears. I can wear these constantly without any fatigue at all.
They're definitely worth a listen, but you'll need to be patient enough to burn them in before you'll be able to hear the advantages of this particular pair. The burn-in time is significant, and truly makes a huge difference.