Like others say, its light, its warm, and cut great. I'm 5'8" and 155lbs and a small fits perfect. Layered with a shell and a base layer and it'll handle some frigid conditions.
Just be careful of the colours. On my computer (apple laptop), the inca blue i bought looks like a dark aqua blue colour, but turned out to be a very dark greenish blue, and i don't like it. I have another arcteryx jacket in copper, and its a wonderful colour, not so bright orange as it looks on my computer but a nice dark copper-orange. The mineral colour in other jackets looked off white to me but turned out to be a pale green.
Dispite the colour dissapointent, a very well constructed jacket, and i'm definitely an arcteryx junkie now.