This is an awesome jacket. For it's weight it is super warm. I have worn it multiple times when the temp is between 28 - 40 degrees and have always felt warm. I just wear a sweater underneath and usually am on the colder side but this jacket definitely does the trick on walks with my dog. It is super light weight and also looks great. If the temps got down to the teens or single digits I would throw on a shell but for all other temps it works very well. Highly recommend this over Patagonia's own nano-puff which is nowhere near as warm but is much lighter in weight.
For the price, you cannot beat this jacket. It's incredibly light and very warm. I've worn it for short periods down into the mid-20s so far with just a t-shirt underneath, and it's performed perfectly. With my Patagonia Lightweight R4 underneath, I'm sure it could go below zero no problem. And best of all, it packs down super small (great for travel, skiing, etc.). I'm 5'9" 150lbs and the Medium fits very well, although it is a tiny bit long in the back for my taste. I got the grey with the green accents and it looks great too.