Huge, Warm, Light, Compact
I love this bag. The only thing I think I would want to improve upon it is at least the option of having some sort of membrane material on the top instead of just the Pertex, as I like to sleep with the tent unvented and have had to buy a BD Winter Bivy to keep the bag dry from condensation.
I'm 5'10" and 155lbs, and this bag is huge! It's good because I only plan on using it in winter when the extra space at my feet means I can stuff clothes and boot liners inside to stay warm and dry out. It is also pretty girthy so you can roll around in it if you're a restless sleeper. There's actually enough room for me to put my 40degree down bag I use in summer inside and still get a lot of loft from both bags, making 0 degrees no problem. I pair this with a liner and it is super comfortable.
I love the center zip. It makes getting into the bag while there's a sleeper to either side a cinch, it's almost like diving in. Getting out is even easier, just start the zipper down and it peels open easy peesy. The foot box zipper is a little small and has gotten caught on the fabric but I don't really use it anyway.