You're not far wrong. The main problem is "design by committee". And I don't mean ten Microsoft guys in a room, I mean the ideas and designs being passed back-and-forth between loads of different hardware and software companies. It's just a mish-mash of needs and wants, and the quality and purpose gets lost in the jargon and marketing-speak like "Feature PCs" (things like powerful tablets).
What goes in their offices every other iteration? Do they get cocky and carried away?
It's all driven by statistics. It's fine getting loads of numbers, but you need to know which numbers to pay attention to. They probably saw that 80% of people now use touchscreen phones with no physical keyboards, so that MUST obviously mean that 80% of people would buy a touchscreen-only PC, even when that isn't what works best for desktop apps or productive working. I would ALWAYS choose to use my computer over a tablet/phone to type something up, use a complex program or to be able to multi-task, that was the main benefit of having a PC, but they forgot that over the buzz of shiny simple touch-friendly apps.
And as for the fact that half of it's missing and there's a very inconsistent half-metro half-desktop UI, well that's just down to the project planning and design forcing a release as soon as apps work and it's secure enough, rather than working hard to make a properly good interface.
I am most definitely NOT a fanboy, but I really can't imagine Apple releasing anything as bad as Win8. Except maps.