They crippled up Explorer in 8.1. The extremely convenient two pane display from XP ain't there anymore. That one had folders in the left hand pane and contents of the selected folder in the right hand pane. Made it real easy to drag and drop files from one folder to another. That's gone. You gotta open a second Explorer window and set it to the destination folder, set the first Explorer window to the source folder and then you can drag and drop from window to window. PITA.
8.1 will run old XP programs. My old AZZ cardfile program in which I keep addresses,phone numbers, and passwords did come up and run. That's a goodness.
They also hid a lot of stuff. XP Explorer called a file a file, and showed every file on disk. 8.1 calls some folders strange and special, like My_Pictures, and doesn't show them in Explorer unless you find a strangely hidden menu bar item, and click down one level on it. I found it by accident and I'm not sure I could find it again. It's much more straight forward to just show all files and folders in Explorer. One big place where everything lives, is simple to use, and simple to code. Clearly the M$ software weenies have had too much time on their hands.
And, the start menu is gone. That was useful. You could group shortcuts to related programs, like anti spyware, or graphics editors, or media players, on folders on the start menu. Made it easy to find stuff, easier than fishing around in Program_Files.