I'm a Commodore guy, but there is one thing I've always envied about Atari ST owners. No, not the MIDI interface. The ST just looks so damn good. To me, it's still a high point in industrial design.
One simple but genius detail about the Atari ST's case design is that the case screws on the bottom have square holes while other screws have round holes. You don't have to learn beforehand which screws are which, or risk loosening things inside that you didn't intend to.
While I know this is common knowledge for people who were around back then I think it's worth pointing out because it's so wild.
The Atari ST was designed by ex-Commodore people. The Commodore Amiga, arguably the biggest direct rival of the ST, was designed by ex-Atari people. (Both lost to the IBM PC in the end.)
The backstory of Atari, Commodore, and Amiga, Inc. is a great one and almost feels like fiction made real.