From my perspective, the worst culprit is GNOME 3. And though I have often criticised the default GNOME 3 interface, with a little bit of tweaking here and there, I have been able to get it to a point where I can actually use it for my daily computing tasks. It is not perfect, but much better than the default configuration. The idea is to make it look like a standard desktop that lends itself very well to using the mouse, rather than mostly to keyboard shortcuts.