MacOS 9 was awful, a product of a rather unpleasant era for Apple really. I wanna say through 9.2.1 maybe even through to 9.2.2 the OS had a nasty habit of corrupting your disk. Hardware-wise Apple used CMD64x based IDE controllers so when OS9 wasn't screwing with your data the hardware itself would.

There absolutely were animations e.g. when closing a Finder window, but they were much lighter weight. As far as I'm concerned System 7 was probably the zenith.

I enjoyed the aesthetic of Mac OS 9 but my experience is congruent with yours. OS 9 had major stability issues and was so, so slow.

To me it’s the opposite, System 7 crashed all the time and MacOS 9 was rock solid. System 7 was a mess until 7.6, at which point it was basically MacOS 8. And the UI was way more pleasing, the system 7 one had a 80s vibe to me.