These headphones sound great, and yes, they seem to be a step up from the PX-100 pair that served me well for 5 years. As before, the bass is surprisingly good for such a small set. But it's not just bass, there is good clarity and power throughout the whole range. Different voices are nicely separated, and you can pump enough volume through them to drown out any environment without distorting (not noise canceling, just ruin-your-ears loud). If you have any lower bitrate MP3s, you're going to start noticing the flaws from the compression that you might not have noticed before.
I love the version with the inline microphone, so I can use it with my phone. The buttons don't work on Android, though (the play/pause button may work, depending on your OS, but these controls are designed for iPhone). They fit a little snugger than the older model, so they get uncomfortable after a few hours, but not terribly so.
I may be the only person in existence who loved the hard case that the PX-100 shipped with. This set ships with a small cloth bag, which is pointless. It hasn't really detracted from their portability (they go in my laptop bag with me), but I liked knowing they were protected in that hard case.
Anyway, they sound amazing, look good, work with my devices, and none of my complaints were worth deducting one star.