It's so good that even Windows has the Linux (optionally) embedded now.
Still like the Windows GUI the best, though KDE Plasma comes close.
Yeah, I mean desktop environment when I say "UI." It's less about customizability and more about stability for me. Dolphin just crashes way too much for me in KDE Plasma. Like, anytime I do a search. I just go to the command line instead, which is unfortunate for a UI.
Compositing with X server is a mess with multiple monitors running with different refresh rates. Need to try Wayland and see if that's any better.
Also the snap-to on the edges for organizing multiple windows isn't quite as smooth. Still a million times better than Mac OSX.
But, it's open, free, comparable to Windows DE, and yeah you're right, much more customizable.
Also to be fair it's been awhile since I've given Gnome or some other DE a shot.