I think the biggest difference is that it is based on Debian and is a bit more conservative. I prefer cinnamon over xfce and in its default even over KDE.
Really, I just assume better hardware compatibility and slightly newer packages from Mint and that's just about it.
Don't read too much into it. There is nothing wrong with MX, Debian or just plain Ubuntu either. In my opinion Ubuntu fixes a few problems Debian has and Mint does the same with Ubuntu. Because apt is widely supported the Debian family is a great choice anyway.