I jumped at this even though I probably don't need another jacket. I'm 6"3' and 200 (and most of my weight is in my legs) and the L is snug, but very comfortable. I'm actually surprised it fits as well as it does as I have longish arms and a very long torso. Were the sleeves any longer, they'd be too long. As it is, they're great.
I wanted something for warmer months as I have a Patagonia Hardshell for the winter. I wore the Vaporshell jacket the day I got it as we had a massive thunderstorm and I needed to put away the chickens, and found it to be very comfortable. My first thought was that it didn't sweat like my Patagonia or my Marmot. The build is excellent, and the fabric feels tough. With that being said, I've never owned any Arcteryx gear, so I can't comment on that debate.
As far as breathability, it felt very comfortable even in a warm torrential downpour. The hood is also adequately sized.
For those interested in ordering one of these jackets, I would heartily recommend ordering a size up if you plan on layering. Otherwise you should expect a fairly slim fit jacket. I got it in Silt/Grenadine after waffling a bit on color, but am very pleased. The red accent is a nice touch on what would be a fairly plain brown jacket.
The last thing to remember with this jacket is that there are no pockets except one located on the chest. This isn't a big deal for me, but it might bug a few others out there.