Really what about it is not designed for desktops, keyboard shortcuts still work mouse still works. If it is because the start screen has buttons instead of 20 tab menus I will ask you what is quicker to search through not to mention program files tendency to sometimes label things by application or company that owns it.
Use it on my pc for the reason of games. I would fully switch to linux within a heartbeat but unfortunate it doesn't have that wider support for those applications.
8.1 is a really nice and most important much faster os over windows 7. Once you figure out how everything works At first glance it's confusing and unstructured for productivity thats why I use linux for productivity and not 8.1. So I'd pick 8.1 over 7 anytime. But still linux > windows.
Really just the Linux Kernel nothing else? Funny you bring up a Linux Distro considering every major one runs an UI similar to Win8, Unity Gnome3. KDE is even moving to a interface based more around searching under a menu then a bunch of tabs for your applications. I like Win8 because it brought the UI closer to the Linux DE I use often.