I have never once has a problem with any upgrade so to say that the upgrade was a dud would be just a little inaccurate. I understand that you are upset and disappointed and I would be as well if it happened to me, but the overwhelming majority of iOS users downloaded and installed the upgrade without any issues at all.
You cannot gauge the overall success of the upgrade by what you read in a support forum. Users with problems come to a support forum looking for help. The successful updaters are happily using their iPads and don't come to support forums to exclaim the virtues of their devices.
I know that you restored the iPad iOS already, but try this. You have nothing to lose at this point.
Settings>General>Reset>Reset All Settings. You will have to enter all of your device settings again.... All of the settings in the settings app will have to be re-entered and it does take a while to reset all of your device preferences again.
Is your iPad still under warranty? If it is, I would take it to an Apple a store and let them fix it or replace it. If it isn't under warranty, make an appointment at an Apple Store Genius Bar and ask them to resolve the issue for you. See what happens. There is no charge for an Apple a store Genius Bar appointment and if nothing else works for you, you might as well give it a try.