Pros: great bass and better soundstage + midrange than people expect from a $170 phone
Cons: no carry case
I took a flyer on them hoping that they'd be a great portable for commmuting and use at work. After more than a year with them, I'd gladly make the purchase again. I have heard others talk about pain, but I haven't experienced any and I have a very large head. I did flex the metal band a bit to minimize clamping force and that seemed to do the trick.
I've owned the older M50s and my wife has the new M50X. The WS99's are considerably better than both: wider soundstage, better midrange, and far deeper and cleaner bass. Many would think these phone might be best for rock and pop, but I have had great success with folk, vocal jazz, and classical too.
The aluminum cups and thin build actually make them lighter than the M50 series, but the materials touch on the 99's is better, without feeling flimsy. These phones are a great all-around choice. You won't be disappointed.