Sizing varies greatly
If you order this shirt, be aware that you will receive one of two versions. One claims to be "slim fit" and one just says "undershirt". The ones that have "slim fit" written in the neck are large, wide, and stretchy. The ones that just say "undershirt" are slim fit and have very little stretch. The medium grey "undershirt" is close to 2 sizes too small and has no stretch. I usually wear a medium with t-shirts. It's a nice shirt if you end up with the right size/version combination. It doesn't have that super deep "girl shirt" v-neck like american apparel's shirts.
If they sold these two versions separately, so you would know what you were getting, I'd give it 5 stars.
Note to Dex: This is an undershirt and 99% of all white undershirts are moderately see-through. The tighter the shirt, the more transparent it is.