Come on now, the Music app is crap, and some of the other Metro apps leave a lot to be desired, but Windows 8 as it relates to upgrade from 7, is actually superior as far as stability and performance I'm finding. The only difference is the Start Menu is now a Start Page, and well, Search is an abomination.
The real problem is apps perform really well on Windows 8; unfortunately for MS, same apps perform as well on Windows 7. Finally got Burnout Paradise 2 with super DirectX 11 graphics (read: Need for Speed, Most Wanted = Burnout Paradise 2 with super DirectX 11 graphics). Great on Windows 8, runs exactly the same on Windows 7.
Office 2013 is the best Office yet IMO, runs super on Windows 8. Runs super on Windows 7.
That's going to be Windows 8's problem until there are great apps for Windows 8/RT/Metro.