I am 5'11", 155lbs and I found the Large to be the right size. I tried on the medium as well, but it restricted movement. Overall, I think this jacket serves 2 purposes, one well and one ok:
If you need a light layer for under your shell. This jacket will insulate well under a shell. Overall it is pretty thin, so it won't get in the way. It also makes a great lightweight standalone for skating etc.
As a light stand alone jacket. This does have a DWR coating, which combined with the polyester outer will shred water ok. I won't call it waterproof, but its ok. My problem with this application is that this jacket is very thin, compared to similar option. It also has no zippered pockets for iphone, keys etc. If I'm out skating that is all good, but for riding I need that protection. I think for the extra $10 in price, the 32 Anchor Joe Sexton jacket destroys this one. It is warmer, has multiple zips, medium pockets etc, and just feel higher quality. This is why I am giving this jacket 3 stars. I've seen the other options and this one doesn't quite match up.