Has a bug report been filed ? Is the problem mainly isolated to nvidia drivers or does it encompass other video systems ? One thing I do hate about upgrades is when they break things that have been working well in earlier versions. My guess is that the problem will be fixed. You might try the upgrade again in a couple of months. Or just wait till Fedora 22 comes out. I usually wait at least a month or so after the official release date before I upgrade. I also apply the upgrade on a test machine before I commit my main system to the upgrade.
What app did you use for the upgrade ? Did you use YUM or Fedup ? Also did you install via an ISO image or via a network upgrade?