Shorter barrel, shorter grip, 8 round capacity instead of 10. I have the compact, and love it. It's not a true compact, like the M&P 9c, more of a Commander size, but it fits my hand perfectly.
My .40 Compact holds 10 rounds all day long. Aside from the slightly shorter barrel and the shorter grip that you can get all your bony fingers around. they pretty much shoot the same. At least to me they do.
I have they FS .45 and I would not get the compact. This gun was meant to be FS. YMMV
How does the recoil of a 45 and 45c compare to a 1911?