I wrote a review on the hoodie version of this jacket, and just bought the jacket version of it. Here is why: I am 5'10" and weight 160 lb. I always wear a size Medium in Arc'teryx. However the Hercules cut is a bit loose and a bit more roomy (without being baggy at all). I found out that getting a size SMALL, was a stroke of good luck. The jacket fits very athletic doing it one size smaller, and the arm length and torso are still perfect. However by having a snugger fit, it keeps body heat more efficiently, and I can use it for layering if I need to. I had originally purchased a Venta AR, in Medium which has a windstopper fabric, but I found that the forearm fit was too loose, and cold air would get in through the wrists. The Venta is not meant to be a bit insulator layer, but it is worthlss if you have cold air moving up and down your sleeves! Also, the neck portion of the Venta was too stiff when zipped all the way up, and the zipper scratched my chin. No problem with the Hercules!!! The high loft fleece feels wonderful against your skin, fits athletically, and I can even wear the size Small Hercules jacket as a layer underneath my Hercules hoodie (M), which I did this weekend at the football stadium! Layered like that it was like a full winter coat! It is not 100% windproof, but it is 95% windproof, and the breathability is SUPERB! Mine is black, so it is quite easy to combine with other garments. I love the fit, and it is warm and super comfortable. It is not as warm as an Easy Rider jacket, but the easy rider is stiffer and way too hot to layer if you are going to be active outside. I love this jacket!!!

This jacket fits and performs wonderfully.
Lightweight, extremely breathable (you can even wear it indoors), form fitting, and stylish to boot. Warmth level and wind resistance wise, with mild activity (even normal walking), this jacket kept me warm in 40 deg weather with 15mph windchill with a T-shirt underneath. I would advise wearing a windproof shell if just sitting around base camp in such conditions, but paired with any level of aerobic activity you will be warm and not overheating.
A warmer, more windproof (less breathable) alternative would be the Arcteryx Easyrider... But its also bulkier.
5'9, athletic/slim.. Small fits perfectly, sleeves long enough, torso long enough.
Versatility, as it works well as a standalone softshell, but also works as insulating mid layer.

This jacket preferred over the likes of: TNF Summit Series Windstopper Thermal, MHW Alchemy, Patagonia R4.