I tried on one of their slim shirts. It's actually slim.
Co-sign on this. I just got one of these in and unlike previous reviews I find that the sleeves were definitely slimmed down. The body was also slimmed down significantly, XS slim fits just like a Uniqlo XS.
Definitely happy with the purchase, and glad to know J.Crew is slowly but surely starting to cater to the modern gent.