The Metro UI isn't actually impossibly horrible from the "regular" user's standpoint. It took my elderly parents all of two weeks to get used to it for running their card games, browsing the web, and so on. But I did install most of the software they would need on the base system; out of the box it really doesn't do much.
Still, they only tolerate the new UI. The still gripe that it's not the same as XP. I'm firmly convinced they'd have been far happier if they'd followed my advice and bought an older Win7 based system that still had the tradition menu-and-window organization.
The best thing Microsoft could do as far as the Win8 debacle goes is to ensure that 8.1 lets you stick with the "traditional" desktop full time. The thing my parents hate the most is this full-screen, one-app-at-a-time mentality from the cellphone and tablet markets. Just because that kind of approach worked for green-screen terminals and iOS doesn't mean that people like it -- just that they used what they had to.
The windowing interfaces used by Gnome 2, KDE, Apple OS/X, Win 95-7, OS/2, and a host of other interfaces were based on years of research at IBM that resulted in the Common User Access style guides. They weren't pulled out of their arse based on some artsy-fartsy desire to just do "something different." They were based on studies and feedback.
Microsoft threw all that work out the window with the Metro menu system in favour of pursuing an iOS experience, forgetting that the only reason the iOS interface is acceptable is because it's designed for small screens. Not necessarily tablets, but small screens.
Metro is an admirable first cut of an interface that would work well on the small screen devices like a phone or tablet, but they didn't go all the way. Every third party application I've used on my parents box drops you back into the desktop when it runs. So in effect, the only thing you get that's "tablet style" when using WIn8 full time is the start menu. Forcing people to shift their entire usage pattern for the sake of a menu system was asininine, and the sales numbers prove that out.
The sales numbers for Win8 are even now grossly exagerrated. Everyone I know who bought a Win8 box save my parents downgraded to Windows 7. Every single one.
Hell, if I were buying a new box I wouldn't buy one without downgrade rights. (Aside from that, my next system upgrade will be for my Linux desktop, not another Windows system. I only need one windows box, and that, happily, runs Windows 7.)