the more I buy from Big Agnes; the more I like their construction, although I wish they made all of their products in the USA. I bought this in mid-spring thinking that I would possibly use it once prior to summer 2012. Never have used it yet until this fall 2012. I will follow up with a full review after my first use.
In examining the bag, I do notice that the loft of the down is quite high relative to the amount of down in the bag, meaning that they have stuffed it with quality down. the stiching and seams are tight. the down collar is shaped quite well at least for me anyways. The fit is roomier than other zero degree bags that I have seen, which is good for my body.
Remember of course, that Big Agnes does not place insulation material on the bottom of the bag, as you insert your sleep pad into the sleeve to act as your insulating pad. a great concept but it does require a pad that fits the sleeve. I have an older, larger Thermorest but my son has a newer Big Agnes pad so I have to use his pad to incorporation a pad into the Big Agnes System. I would not recommend using another pad if it does not fit ino the sleeve as your back would great chilled when you roll onto your side.
Overall, build quality is high with great material used in construction.