I have long regarded the Macintosh as the single most significant innovation in the history of computers. Computer mice and Graphical User Interfaces (GUIs) had been used in specialized applications before, such as in 3D modeling. For example, here's a CAD program running (with a mouse) in MIT's CAD design lab in 1982. (Though this video is posted by the SolidWorks channel on Youtube, I believe it pre-dates SolidWorks.)
Most personal computers didn't even have that interface, relying only on the keyboard. This was the state of computing in the early 80's.
The Macintosh was the first commercially available personal computer to recognize the importance of windows, buttons, and graphics, and to be designed for the mouse.
I recently had the opportunity to visit a friend who has a working Macintosh SE. It was my first time seeing one of these computers working in person.
Possibly the most surprising thing to me was the screen. It's difficult to put my finger on it, but it made amazing use of the black and white display. Honestly, the experience was significantly better than using a Macintosh emulator displaying the same graphics brighter and crisper. I guess it shouldn't be surprising that the interface looks best on the screen it was designed for.
Speaking of the screen, historically, one of the things that the made the Macintosh revolutionary was the use of white-on-black. Earlier computers relied on green or similar phosphorus colors on a black background.
One of the most interesting things for me was how much the interface resembled the modern macOS. The menu-bar has some of the same entries with the same keyboard shortcuts denoted in the same way. But even the way you could interact with it was the same. I could double-click on a word to select it and drag around to select by word. I would have guessed that that piece of interaction was much more modern. Now, this particular computer was running System 6, so it's possible some of these similarities don't go back to 1984. But it that doesn't detract from the point that the macOS interface isn't just inspired by System 1, it borrows huge sections of the UI.
The first takeaway was that the usability of my computer today is not the result of 30 years of iterations. But rather, much of it is due to the genius and vision of Jobs and the original Macintosh design team.
My second takeaway is a changed perspective of this older technology. I approached it like I would a typewriter—something of historical but not practical appreciation. But beyond specific similarities to modern computers, the Macintosh SE proved much more practical than I initially would have guessed.