I live in the Northwest and rain seems to come at any time so down is only practical in the mountains mid summer, or the dead of winter. I have had several down jackets and many synthetic jackets. This jacket is the best of both worlds! Like other reviews stated it doesn't breathe as well as the black diamond first light hoody or the competing Patagonia version of that jacket. That said it is a MUCH warmer jacket. Over the years of Alpine climbing I have found that I rarely hike in my insulated jacket, so essentially my jacket becomes a belay parka or for when stopped and taking a break. This jacket fits that bill perfectly. It is ultra light (feels like a down jacket in hand), the DWR is excellent, still very warm when wet from rain and leaking through (not suppose to be a rain coat).
Liner is smooth which means it slides on over my Patagonia R1 perfectly. The belay zipper allows the Hem of the jacket to keep your backside warm while having good access to your belay device and harness. No more bunched up jacket between you and your ATC. I didn't realize how much I would appreciate that feature, and can't believe other brands don't add it. So over all this is by far the best synthetic jacket on the market in my opinion, especially if you run a little cold like me.
I'm 5'6" and weigh 149lbs athletic build. The small was to tight around the chest, but the sleeves on the medium allowed air to blow up sleeve (easily remedied with a little stitching to fit my dainty wrists ) since the slight modification this had been the best insulated jacket I've owned ever! Oh yeah I forgot to mention that after being in a down pour and water leaking through, the jacket dried out in about 45 minutes! If you have been looking at this jacket and noticed it rarely goes on sale, there is a reason for that. It's simply amazing! If in the market, buy this jacket!