Vista had many problems because of it being TOO much for the vast majority of computers on the market could handle at the time. For example, the biggest problem was the inclusion of Aero which required a 3d graphics acceleration chip of some sort. The problem was, the vast majority of computers out there for the average user didn't have any form of 3d acceleration. You couldn't get rid of aero or other interface options at the time that required it since too much in Vista was interconnected. So if you didn't have the hardware in your computer to support vista, it was going to be unstable POS for you.
Windows 7 fixed the connection problems, but in turn, the push for at least minimal 3d graphics acceleration has produced many main stream computers since then capable of handling windows 7. There were other things 7 got right that Vista was a bit wonky on, but I don't want to go into that fine of detail in this post.
Windows 8, improves upon the foundation of 7, but really missed the mark with user experience. I installed 8 and there are just WAYYYY too many annoyances as a desktop user with a keyboard and mouse only input with multiple monitors that really just annoys me. It took some custom themes as well as having to do many work arounds. Like creating quite a few shortcut "apps" for launching some things with a 1 button approach. The average desktop user isn't going to stand for that.
What would have made 8 successful without a huge change? Allow users during INSTALLATION the option of using the start screen with the tile apps or to use the old start menu system. Have them both there and give the user a way to swap between them. Include the new stuff, but EXPLAIN IT and what parts are being installed during installation. Give easy access for users to turn it off.
Oh and give Aero Glass back. Many people got used to and liked the transparency look from Vista and 7. Also, making all the default themes look like some 70's art show with everything being all blocky, no drop shadows, pastel colors EVERYWHERE, and little contrast between items on the screen is just bad. Style wise, it feels as if windows 8 went back in time and I do not like. If some head hancho at microsoft likes that look then include it, but don't remove other options that were previous in windows 7 and vista. I don't mind having the ugly pastel theme as the default them as long as I KNOW I have the option during installation to change it to something I might like different.
That's where windows 8 missed the mark. It does great in trying something new, but fails hard in forcing users into the new experience. Speaking of which, much of the new interface for windows 8 is not very intuitive at all.