Typical Stoic review: High quality, weird fit.
The Large in the Stoic merino t-shirts fits me pratically like a second skin, so I ordered a large in this shirt, but it is too big. The sleeves fit ok; semi-fitted and long (3/4 way to the elbow!), but the chest of the shirt is too large (bagging at armpit area). I would probably keep it if this was going to be my outer shirt but I figure it will often be my only layer or undershirt.
I'm exchanging it for a medium because the shirt is super light and comfortable. Hopefully that fits better. For reference I'm 5'9" 165lbs, 42" chest. Beware hairy chested dudes - this is so thin you can see the hairs poking out!
*edit: Received the medium, fits great.