Yeah, 8.1 really isn't awful as long as you bypass the start screen bullshit. The start times are stupidly fast, too. With UEFI boot and a Corsair MX100 256GB SSD, my laptop boots up in a matter of seconds. It's just nuts. Even my pussy little HP Stream 7 tablet boots up quick and you can't get much lower-spec than that.
I think I sort of get what happened with Vista and 8. In Vista's case, the OS had a rocky development cycle. It was in development for a couple of years, got bloated beyond belief, and then they basically restarted the entire project and cranked out a workable product in a fairly short amount of time. The core of it was decent, the security was drastically upped from the disaster known as XP, but the optimization just wasn't there. On a decent machine you couldn't even really tell much of a difference between that and XP, especially with SP1 and SP2.
With 8, I think Microsoft was suffering from arrogant management and a serious case of Apple envy. They wanted to take the tablet market and strengthen their desktop hold and they figured that convergence would be the way to go. I think the biggest proof of that is when they tried to put the Surface against the iPad. That marketing campaign failed miserably. Their recent effort to bash the MacBook Air seems to be going just as well (hey Microsoft, you know what I can do with my MacBook Air that I can't do with a Surface? Use it on my fucking lap!). Let's not even get into their strange belief that your average keyboard and mouse user (or trackpad...ugh, trying to use Metro with a trackpad on a high resolution display is not an experience that I want to relive any time soon) would jump at the idea of using a pointing device to control a tablet interface.
I think the failed Windows releases are more Microsoft's recent attempts to stay relevant than anything else. We're not living in the same world that we were when 98 and XP were released. Apple's market share has been continuing to grow, more people are embracing the penguin, and a whole crap ton of people are using their iOS or Android devices more and more in their daily lives. Vista was largely an attempt to modernize NT's security from something that worked in a controlled enterprise environment to the chaotic home environment. 8 was largely an attempt to improve the tablet support from XP, Vista, and 7 into something more modern. Both of them largely succeeded in their base goals (let's face it, Vista was a hell of a lot more secure than XP and 8 is actually a really nice pure tablet OS), but they both fail pretty dramatically in other ways.
Also, I just remembered that I was supposed to get you some Windows 10 screenies today. Whoopsie.