I've been using this shell for over two years; it has done great things for me. Most of its use has been climbing related - the material is comfortable dynamic, and sufficiently durable. I would have expected greater signs of abrasion from the rock, but it has held up surprisingly well - no loose threads, no disconcerting fuzz. The hood fits well over a helmet, and the stiff brim provides helpful direction for falling rain. The jacket breathes well, and repels water to the extent that would rightfully be expected of it; eventually it wets out, but it is not a hardshell. I am 6'2", 175 lbs, and a large fits me relatively well, since I am usually not layering anything of significant bulk underneath it, though I would prefer the length of an XL, were it not for the (for me) disproportional increase in chest width employed by most American outerwear companies, such as Mountain Hardwear. Overall, I would give this jacket an emphatic 4/5.
My boyfriend loves this jacket. It is waterproof, resists the wind very nicely, and it is warm. He has worn this running in the winter, and it kept him very warm and was lightweight enough that he wasn't too warm. If you are out in temps below 30 or so and aren't working up a sweat, you will probably need another layer under it.
This is the perfect mid-layer jacket! I originally went with the MH Thermostatic, but was really unimpressed with the durability of the outer layer, not to mention the jacket's fit was very "frumpy." This jacket, on the other hand, is sturdy and warm, perfect for activities like climbing or biking. I'm not at all concerned with the Principia rubbing against some rock while climbing or snagging a branch hiking - it holds up! If properly layered, this jacket can function well as a top-layer in cold/windy temps, but also is slim-fitting enough to be worn underneath a heavier jacket for maximum warmth! I'm 5'7" 145lbs, and the Small is perfect!
I've had this jacket for just under a month now, and I'm in love. Keeps you warm in cooler temperatures, and blocks most of the wind. Spent a day climbing in this jacket in cool 40-degree weather, but saw 15-20mph gusts. I stayed warm all day long. I did a lot of crack climbing, and the cuffs and arms are still 100%. Buy it. You won't be sorry.