Pros: Good bass, decent mic, low cost
Cons: construction could be better, reliability issues
I'm on my third pair of these, and that's mostly because I'm hard on them. Sound is fairly uncolored, though brighter than my reference Grado SR-80s. They respond well to being driven by a decent amplifier.
The trick to getting good bass out of these, like most in-ear units, is getting a good seal. They come with several sizes of pads, for me the larges works. Without a good seal, you get poor bass and low isolation, but WITH a seal, wow!
The mic works well on my iPhone 3G and 4G, the control button could be more positive, but once you learn where it is and how hard to press it, it's ok.
The downside to these is the construction, which is a bit flimsy. I've had the cord break at the plug entrance, had to replace the plug. I had another cord break at the mic/switch when I got the cord snagged and tugged it. Otherwise, at the price, they're disposable.
Which brings me to price. At their list of $99, not a great value. Good sound, but not quality. But, who pays list? Got mine on Amazon for $35 for the first pair, $18 for the second pair, and $25 for the third pair from independent sellers. All came in the original Sennheiser packaging, all sounded identical.
Best sounding $25 headset out there, no question! At $100, still good sound, not a good value.