See, the devil is in the detail. I need High Contrast Themes because I have only 40% vision and cannot decipher anything on a white page. But In W10 this has not yet been fully implemented. The whole Settings area and some other areas do not work in high contrast. I assume they eventually fix that, but for now I can only make very limited use of W10.Windows 10 works now. (except for those that find it does not work for them)
Many have chosen to use it as their primary.
I have found it fully functional and a nice system to use.