Love the bag. Very light, and packs tiny. I have taken it on a 3 day backpacking trip, so this is no long term test. I have not experienced down leaking, and the zipper doesn't seem worse than others.
I think the major thing missing is a neck yoke, which seems to have been fixed with the new REI Igneo bag. The lack of this feature makes the bag drafty, and therefore cold if you try to push the limits of its temperature rating. Of course, you could always place a piece of clothing on that area to stop the draftiness.

I love how light and compact this bag is. I've found it to be true to it's temp rating. The only grip I have with it is it's a little tight in the chest area but it's not a deal breaker. The bag does feel like it's pretty delicate but good luck finding a super light down bag that isn't. Overall I've been very pleased with this bag.

I recently purchased this sleeping bag as I've grown tired of lugging around the Big Agnes Farwell. I was very pleased that it was about 1/2 the weight and about 1/3 the size of the Big Agnes bag. I just spent 3 nights in the Sierra with one of the nights around 11,000 feet where the temps dropped down to the high 20's. I was perfectly warm without thermals. Those that are complaining about the warmth of this bag may not be using an insulated pad, (I'm using an ExPed 7).
I have two minor complaints. First, the stuff sack is ridiculously big - you can probably put two bags in the stuff sack. Secondly, the sleeping bag is a bit on the narrow side. I bought the extra long as I am 6'3" and about 225 lbs; it was a little tight but nothing too uncomfortable.
During this short period, I have found the bag to be a solid buy based on the size, weight and overall performance.