Windows 8 was a first step. Windows Phone 8 and the Xbox One OS (there are two in fact) were still differents OS, even if they have common parts.
I have it on 2 tablets and one of my workstations and to sum up my experience with it: It's awesome! Nothing else even comes close.
It all starts with the most basic interactions. For instance - there's no other window manager that lets you completely control the OS with just the keyboard and in such a consistent, logical and discoverable way as Windows.