I just upgraded from Windows 8 to 8.1, however, after doing so, I found that my HID-compliant USB gamepad (an SLS USB Sega Saturn Controller, fwiw) was no long functioning properly. Looking in the properties in the control panel, I found that the x and y axes do not move when the d-pad is pressed; buttons 2 and 3 do not seem to respond; and if button 1 (or 4) is pressed, the indicators buttons 2,3,6, and 8 light up and do not go off. This pad worked perfectly in Windows 8.0, and just to make sure it wasn't malfunctioning, I tested it on the computer downstairs running Windows 7 and it worked fine on it as well. As such, I can only guess that Windows 8.1's HID driver has a bug.
Given that this is a generic driver, I'm not sure what I can do about it other than wait for it to get patched, but I wanted to make sure Microsoft knows about this.
Of course, if anyone knows of any fixes, please let me know.