I've tried other Castelli shorts, and I've never been a fan of the KISS chamois. They always felt, to me, like I was wearing a diaper. However, the pad in these shorts is probably the best I've ever worn. It's nice and thin, yet very dense. In fact, the first time I wore them (on a 20 mile ride) I never even felt a bike seat. I can say, with absolute certainty, that I've never before worn a set of bibs that make the saddle of my bike literally disappear underneath me. For comparison, I've also ridden Giordana FormaReds, Rapha's, Assos Mille, and none had a pad as comfortable as this. Now I haven't ridden them 100+ miles yet, but they're still incredibly comfortable even after a metric century.
The pad is also very low profile, so you don't feel like you're wearing a diaper. I also love the super low cut front, as it makes taking a leak a very simple affair. Hunching over or sliding bib straps off the shoulder is totally unnecessary.
The material of the short is very supportive. I have a 31" waist, with rather large 25" diameter thighs, and a medium fits me fine. It's tight, but it should be tight, as these are intended to compress your muscles.
One warning, the light gray and white versions of these shorts are VERY revealing. While the fabric isn't transparent, it's thin and clingy enough to shrink wrap your junk like a sausage casing, leaving NOTHING to the imagination for anyone standing within 50 feet of you. The amount of detail these reveal about your man-bits is shocking actually.. borderline pornographic. I tried both and immediately sent them back. However, the black/anthracite model looks great and feels better.
If I had to list one negative about these, it's that the chamois isn't sewn in with the same sort of care as the rest of the short. The simple zig-zag stitch isn't terribly secure, and I've already had to warranty one pair because a stitch around the pad started to come undone.