In my opinion, the biggest failure of windows 8 is that they called it windows. If metro mode was an installable add-on for windows 7 that you could jump into whenever you wanted a simplistic or touch-friendly experience, people would love it. The usability isn't terrible on its own, it's only terrible if you try to use it while expecting a windows operating system.

for example, the only being able to run one fullscreen app at a time thing. the proliferation of iPads has shown us that users love this, in the right context. The desktop PC just isn't the right context.