Firstly, the price of this piece is just right if you understand the sweat equity Arc'teryx invests in every piece of their gear line. This piece is no different; a perfect mixture of Gore-Tex Pro Shell reinforced in the high abrasion areas of the garment, the neck, the shoulders, and the arms and the ultra lightweight and durable Gore-Tex Paclite throughout the body. The stitch count is easily 25 per inch and the jacket is completely seam sealed. Most times, having a zip away hood, this one is helmet compatible by the way, makes you look like you're wearing a neck brace. Not so with this one, very reasonably sized stowed away and very easy to unzip and throw over your head.
The concept is great between Pro Shell and Paclite and here is why; heat rises, and while Pro Shell is a more durable fabric, it breathes better than the Paclite, so as you are pushing yourself the heat is rising up through your shoulders, neck, and arms and is able to breathe easier because the Pro Shell is in all of those places.
This is a very bombproof jacket, best of it's kind for how light it is (13.1 oz in Medium!) and the nice part is it covers your bum for the nastiest of storms, but it isn't cut as long as it's cousin the Theta AR. It has one handed pull drawcords around the waist, velcro tapered cuffs for your wrists, and a fully adjustable and stowable hood that can cinch down tight and block out the windiest snow/rainstorms.
The best part about this jacket for me is that it is only 2 ounces heavier than their Beta SL but can withstand FAR more abuse in the mountains. It packs down to 1/2 the size of a 1L Nalgene, basically a softball in size Large which is what I wear. I am 5'10" 205 and it fits snugly over my Montbell Permafrost Light Down Jacket if the mercury really drops. Ideally, a baselayer and midlayer will be perfect and you'll have just enough room.
I have several Arc'teryx jackets and I can truly say that they are the best jackets out there for their specific activities. Few come close, but if you want the best, Arc'teryx is the answer.