The most productive environment I've ever used is Gnome 2 using Compiz. It was incredibly easy to flip between windows. Compiz has since been abandoned and only the most die-hard fans try to fudge it into working on modern systems. I gave up after Debian Squeeze and just started using tmux instead. I felt that Linux was losing it's way after that.

Eventually I stumbled across Cinnamon (and/or Mate) with hotcorners and tmux. It doesn't have the previous configurability but it's still pretty good.

The reason people held onto XP for so long was that it just worked well and it was consistent. Many of the Linux GUI people should take that to heart. Instead they always seem to try to be in catchup or trying to surpass Windows. Gnome 3 and KDE 3+ have been so very unwieldy, resource hungry, or lacking in features. They've been the Windows 8 equivalent of the Linux desktop.

Even to this day, most people don't like the Metro style interface (unless they are playing with it on a phone). I'm blown away by how difficult it is becoming to use Windows. I will go into the Metro style settings and see that a configuration option is not present and then have to go into the good ol' control panel. Or vice versa. I'm getting increasingly drawn towards using Powershell by default so I don't have to backtrack.

Windows has been trying to force new "UI paradigms" to sell more copies of Windows. Linux should realize it doesn't need to adopt the new and flashy... unless it really is an improvement.