I'm very finicky with the way my desktop works, for example, I want each window to always start maximixed in the same monitor, and I want its siblings/dialogs to follow suit. I want a different desktop background for every monitor. I want independent docks for every monitor, each with different widgets, and a few other small things.

Gnome is rock solid, but it can't do any of these things, and some aren't even possible to do manually. KDE does, but it's less stable, so every couple of years I try Gnome again, only to switch back after a couple of months. Gnome is not ugly, it's actually elegant in its simplicity, but it's too plain, too vanilla.