I have to say, when I first put on the headphones I expected them to blow my socks off. Coming from HD598s - considerably less noteworthy headphones - I was offended by the almost tinny sound of the IE 600s. But after a day or two I was able to adjust to the sound (but still not quite fully). There are definitely some tracks that play very nicely with the IE 600s, namely vocals and real instruments. Sadly, most of my music is electronic music that seems to be mixed too harshly in the high end for listening with the IE 600s.
The fit is decent, it did hurt my ears slightly as I got used to wearing them (even after finding the best fitting tip), but that seems to subsided slightly. I find doing voice calls with the IE 600s very difficult because my own voice reverberates through my ears in a jarring way.
The build quality is good, the earbuds themselves are well designed and I like the look and feel. I wish the wires that come in the box, however, were some kind of threaded wire for durability and tangle prevention. It's just something I'd hope for at this price tag.
The carrying case looks good but the inner design could probably have some more compartments for keeping the buds and wires separate and secure, and perhaps a sleeve for the cleaning tool. I also have a problem with the zipper, it came in a state where it often gets stuck. I think a slightly looser fit for the case would help the zipping process without sacrificing integrity.
Overall, I enjoy listening to music with the IE 600s, but I wish they had really blown me away. I nearly returned them to get the IE 300s because I guess the 300 model would give me enough to make me happy without blowing me away, which is what I got with the 600 model except at a much steeper price.
At the end of the day, I admit I'm a loyal Sennheiser customer. As long as I can rely on the build quality and trust that I'm getting what I pay for in terms of a listening experience, I will always buy a Sennheiser product when I have the choice. On that note, I will be buying one of your high end open back, over-ear models at some point in the next year or two... Is this the time where I ask for some sort of discount? Haha, just joking - but please do keep up the good work and I hope my feedback helps the team in some way. Cheers!