I bought a medium for my husband, who normally wears  men's medium shirt, but it was way too big.  It was also too big for my brother in law, who normally wears a men's L/XL shirt.  So, I'd say these run very, very large.  The length was right, but the chest measurement was off.  My husband was very disappointed that there wasn't a smaller size available.

The reason it got two stars is that it has really nice soft shell material on the outside and fleece on the inside and looks great in person (if it fit).

So, if you normally wear a men's XL, order the medium and it should fit great.