As always, thrilled with Backcountry's customer service.
I'm 5'8" and 125lbs. I usually wear and XS-S and got the jacket in XS. It fits perfectly. The sleeves could be an inch longer, but I think its probably just because the puffiness of the jacket makes them ride up a bit at the shoulders. If I tighten the velcro around my wrists, they fit just fine.
The fleece lining makes the jacket even more cozy-warm. Perfect alone for a chilly day, or with layers underneath when the temperature drops below freezing.
It isn't the most form-fitting jacket, but for a down, its one of the least-michelin-man ones I've seen yet.
Overall, its a great price for an excellent jacket.