I purchased this jacket for a three day kayaking trip in Yellowstone. It rained/poured all three days. This jacket kept me dry both on the water and at camp. It is NOT meant to keep you warm but to keep you DRY!! When I first had to put it on I did feel the warmth from the Omni lining but it was the layers underneath that kept me warm. It helped block some of the wind on the water but it is NOT a windbreaker. Even during a windy row with misting, I was warm and dry with just my UA heat gear shirt and this jacket.....but I was rowing so that helped with the warmth. It works great over a few layers.  The hood also worked great pulled over my ball cap while rowing through a rain storm!  It finally did get a bit soaked on the bottom due to the water coming in through my spray skirt but it dried by morning and was ready for another wet and windy day.
I could not be happier with its performance.

I ordered both the medium and large and kept the large. I wore layers consisting at times of a single UA long sleeve heat gear shirt to a silk turtle neck, a quick dry t-shirt AND a fleece pull over and had plenty of room to row. I am 133 pound, 5'6". I just felt the large gave me more layering ability. If I were to wear just a single shirt, I am sure the medium would have been fine. I do think Columbia runs a bit small. And the colors are awesome:-)