I like this jacket because it packs down extremely small in your pack, weighs very little, and packs a surprising amount of warmth for its size. I found myself picking this over the much bulkier Phantom 800 jacket (MH) just because it takes up so much less room and is almost as warm. Its a must if you plan on layering up on your next backcountry trip or need a jacket "just in case" it gets cold on your next alpine summer adventure.
I bought this jacket as an insulated layer for a bigger puffy jacket. The idea was that together they would be warm enough for sub-zero temperatures, but I wouldn't be saddled with one enormo jacket that might be too warm for the warmer-cold temperatures. In the end, I wore this jacket much more often than the bigger jacket, because this one is so light and warm. You can't believe how warm it is, because it weighs almost nothing. I read that it had a "slim fit," but I found that it fits true to the other Patagonia down jackets (the Nano, the sweater, etc.). For me, Patagonia jackets run big - I bought this in a Medium and still have some room, even though in most other brands I am a Large. This jacket packs up into nothing, and comes with its own little stuff sack. I got mine in black, and it is VERY shiny. It's probably too shiny for me to wear on a regular basis, but maybe you're looking for something with a little flare. Either way, I love it.