I received the jacket just in time to take on a spring trip to Grand Teton National Park. I'm 5'6", 170 lb and very broad shouldered. The large fit well enough to allow for layering a lightweight fleece or puffy with just a bit of snugness across the shoulders and arms. The body was loose but not comically baggy like other, more boxy, jackets.
The Gamma LT is extremely well constructed and the lightweight material is soft to the touch with a bit of stretch. The main zipper did not operate as smoothly as I would have expected but there were no issues. The inner zipped pocket is a bit small as it didn't fit my iPhone XS.
On the trail the Gamma LT was highly wind resistant and weather resistant enough to not wet through with sustained light rain or a brief heavier shower. Breathability was good for moderate exertion hikes in low 50F to low 60F temperatures.
It also worked well as a casual jacket while hanging out in Jackson Hole.