The wool lining on the USMC is annoying as hell, took it right off. The arms are pretty slim on me and I kept pushing the lining out through the sleeve. I got it right with some adjusting, but it ain't worth the hassle in the mid-60's of Arizona.
I don't think the fit of the jacket is particularly boxy, although I'm typically in between a med and large and I took a chance on a medium in the USMC. Any smaller and I'd have maneuverability issues but I think the trim fit is appropriate with this jacket. Guess I'll crosspost these: