Well, Windows 8 is a capable OS too. It's just got a somewhat awkward and unfamiliar graphical shell.
I don't even hate the Windows 8 shell; I pretty much take it for granted that modern desktop shells suck. That's because designers keep trying to get them to do more for users, when users don't really need *more*; they need the shell to do what they want, when they want it, and then stay the hell out of the way. On top of that there's the unfamiliarity. Windows has always UI problems with putting a cheery facade over a complex train wreck, but the fact that they keep changing the signposts.
I just roll with it. It's like learning to conjugate irregular verbs when you're mastering a language, only they keep changing them every few years. As an *OS*, apart from the somewhat confusing shell, I have no complaints about Windows 8, unlike Vista, whose aggressive "optimizations" broke a number of tools I use regularly. It's all increasingly peripheral, anyway, as more information is managed through the web. The desktop is no longer the focus of the user's experience, it's just a terminal.