In some ways Archimedes' RiscOS was ahead of its time, in some ways it was a disappointment. It never matured due to lack of momentum, market share.
I suppose that most of all, it reminds me of time when actual, genuine real innovation in UI design was still on the menu.
It was really interesting, like a third way of doing things that wasn't "windows" and wasn't "mac".
The OS being on ROM made booting insanely fast. Like 2-3 seconds from cold start to the desktop.
Programs were actually folders, like modern macOS, so you could poke around at how they work. BASIC was still a thing, and I remember being able to edit the BASIC source code of some programs. Felt like "view source" did for the web.
Plus nothing has ever come close to the blue mouse cursor :)