Windows 7 was for most of us, the gold standard in Windows usability, stability, and a great user interface.
Windows 8.x is/was actually better in resource management and very stable, but it hung it's biggest constituency (desktop users) out to dry.
Windows 10, looks like it attempts to fix the 'bridge too far' mind set that brought us Windows 8, so that's good, but I'll have to wait for the release version.
Give people the choice of interface, that's what MS fumbled.
I'm a mac user most of the time, and there's a button on the dock that will let you make your desktop look like the home screen on an iPad. Do I want that ? Nope. But if I want it, I can have it.
And the last version of the Mac OS was a free download, and this next one will be too.
So, if Apple can give it's OS away AND give you a choice of which user interface to use, then Microsoft, who will charge for Windows 10, should be able to let you decide whether you wan to use the Modern UI, or the desktop. Apparently you can do that in Win 10, but, MS, you could have save everyone a lot of frustration and yourselves, a lot of lost revenue if you gave your users what they want, choice.
And then you wouldn't have to do something hokey like skipping an entire version number (9) to put some distance between yourself and Win 8.x (aka Vista 2).