The sticking point for me with Unity was switching between multiple open windows. I typically have a dozen or so terminals and gedit and Chrome windows open across a half-dozen workspaces, but if I want to bring (let's say) a specific terminal on my current workspace to the foreground, I couldn't figure out a better way to do it than to open up Unity's display of all the many terminals I have running and try to pick out which one I mean.

I'm open to trying it again once it's had a bit more polish, but I'm sticking with Gnome classic for now.