Back in the day, Kaleidoscope schemes and later appearance manager themes were one of my favorite things about owning a computer. Combined with Classic Mac OS extensions it seemed like there was nothing you couldn’t do when it came to customization. Even modern desktop Linux, as vaunted as it is for its customizability, struggles to compare.
Now of course Classic Mac OS was a security nightmare but I wish that a modern OS would try to replicate that incredible level of flexibility in a more secure manner. Will it be difficult? Sure, but I don’t think it’s impossible. I believe that something resembling the “app extension” architecture employed by modern macOS which runs extensions as sandboxed processes which are given access to special APIs would be a good starting point.
CWM + window search + keybindings was and it's still superior to whatever theme you are trying to apply. I have a patched Zukitre GTK2-3-4 theme with custom ~/.Xdefaults. I nearly don't need neither decorations nor a taskbar. Just hit win+w, begin typing, your window it's there. Magic. I don't even need to use a mouse.
OTOH, yes, Gnome's blandnes sucks a lot. With Plasma and a bit less, XFCE, you can do far more with a desktop, even Budgie it's far better than Gnome3.
And I miss tons of GTK2 themes from its era. Bluecurve looked better than everything from today. OSX, Windows, Haiku, whatever. That theme looked colourful, positive and extremely usable, with proper and visible menues, buttons, scrollbars and so. Nowaday both OSX, GTK4 with Adwaita (far less with Zukitre) and Windows are a nightmare on usability.
Once you disable the overlay scrollbars under GTK4 and force the GTK theme to Zukitre (once installed) at /etc/profile.d/gtk.sh (a line with 'export GTK_THEME=Zukitre'), most of the dumb choices from Red Hat/FreeDesktop go away for the average Joe user.
Zukitre has gray widgets (not full white, damn UI pseudo-designers), usable buttons and proper scrollbars (again, disable the overlay settings for GTK). And, for sure, COLOR CONTRAST, damn it.
Mac System 7 did it fine; so did Platinum under Mac OS 8-9. Neutral gray colors, usable widgets. Ditto with OSX, but the stripped bars sucked at first, yet Tiger and Snow Leopard look perfectly usable. The same with Windows 95, even Windows XP and partially 7. Windows 10 is unusable with flat widgets with no contrasts and hints for Windows. Windows 11 it's even worse. Current MacOS, with the same overlay scrollbars and lack of contrast it's a huge downgrade from Snow Leopard.
Even the old Motif/FVWM under Unix had a nightmarish usability for the non-CS student, but it had 3D widgets on Motif/Athena (Xaw3D) and grabable window borders.
Go try resizing a window under Gnome3 or Windows 10. Or moving a window at a quick glance.
UI designers should stop following trends and just give up on merging tablets and desktops. It doesn't work.
Now of course Classic Mac OS was a security nightmare but I wish that a modern OS would try to replicate that incredible level of flexibility in a more secure manner. Will it be difficult? Sure, but I don’t think it’s impossible. I believe that something resembling the “app extension” architecture employed by modern macOS which runs extensions as sandboxed processes which are given access to special APIs would be a good starting point.