Here is my story:
10.4 Tiger UI always looked nice and simple for me when i saw it on other computers, but i personally never used this system in real life.
10.5 I started from Hackintosh Leopard and somehow liked it's refreshed UI with gray toolbars, easy readable text, sexy transparent dark hood elements and dark flat dock in 2D mode.
10.6 Snow Leopard was near the same but less buggy and with simpler animations. It also had badly redesigned Expose (currently renamed to Mission Control) which for luck could be returned to normal by some
known modification.
10.7-10.9 Starting from this version strange things start to happen. UI became redesigned to low contrast look with hard to read gray text on gray toolbars. So i decided to skip it until next redesign. The only new thing that i liked in that system where flat scrollbars, so i decided to create
flat toolbars UI mod for Snow Leopard.
10.10-10.13 So i skipped all versions till Yosemite release. Flat UI concept was somehow interesting, but new stupid
iOS7-like icons where total trash. So i skipped Yosemite as well because it was buggy as hell.
10.14 When Mojave was released i made some hardware upgrade and started to use it. To make it look "right" i modified it with system icons from 10.9 Mavericks and also used cDock, XtraFinder, Tiles and some other customization apps and hacks. Still use it as my main workstations system.
10.15 I skipped Catalina because 32-bit apps and drivers for my some of my hardware became not supported anymore. Also i didn't like new system restrictions.
11.0 I skipped Big Sur because i didn't like that new redesign and too many bugs. iOS-like elements mixed with Mac. Too rounded, too bright.
Near impossible to customize system icons. I can write a lot about this UI, but i really don't want. Structure and feel of original Mac UI idea was lost. Also FireWire was not supported anymore, so it can't work with my studio sound card.
12.0-15.0+ I installed next versions just for test, but didn't see any improvements in UI. I hoped that something could changed and improved in next big UI redesign, but... Redesigned 26 beta now looks even more eye burning white, more rounded, more unpractical and iOS-like.