First impressions (about features -- will post later about how it holds up):
Mid-weight (~1.5 lbs.?) parka, designed for snowboarding and downhill skiing. Or so North Face thinks. I bought it to back up my best parka purchase ever, a 10+-year-old REI Gore-Tex parka that's no longer made (and irreplaceable).
Unlike that lighter REI parka, I wouldn't use this as a raincoat for warm-weather biking or hiking. But it seems fine as an all-purpose rain/wind parka for cool-weather use. On 20-degree (F) and colder days, my REI parka keeps me warm with just a sweater and scarf underneath. This should be at least as toasty.
Reasons for choosing the Decagon:
1) Sturdy 3-layer construction. Has a durable woven-nylon outer shell, and a full liner. The liner should delay the middle, waterproof HyVent layer from delaminating. (We have four unlined, ultra-light, low-cost "HyVent 2.5-layer" shells from The North Face Outlet. Two have started to delaminate, after giving good service: The inner layer is flaking right off. Although interestingly, they still keep out the rain. The other two are in reserve.)
2) Pockets -- lots of 'em, outside and inside. These days, you can either get Gore-Tex or you can get pockets. Here's what the Decagon offers: Side handwarmer pockets with fleece lining, zippers, and Velcro'ed flaps. Two breast pockets, with Velcro'ed top flaps. Diagonal pocket on left sleeve, with similar flap. Vertical-zip pocket behind left breast pocket, designed for an MP3 player (has headphone port), but also handy for phone, camera, or subway/bus pass. Padded pocket on inside right, clearly designed for phone or camera. Kangaroo-pouch pocket on inside left, designed for goggles, but large enough to keep a book or newspaper out of rain.
These parkas are sized generously -- in both length and shoulder/chest width. I wear M, but normally upsize rainwear to L to get extra length and to accommodate inner layers. But the Decagon's M and L both seemed to fit me equally well.
About the mystery "thermal" lining: There's a very thin layer of fleece around your upper torso -- chest, neck, and back, but not underarms (where there are pit zips). This seems designed more for smooth/cushy feel, and durability, than for extreme warmth.
The snow skirt is a minor nuisance if you're not using this for downhill snowsports: It includes a serious elastic, so it adds a bit of weight and bulk.