From what I've seen on other forums it seems painless when done from within Win 10 which you can only do for 30 days and then that path is destroyed.
It was a lot more painful for me because as I had no intention initially to revert, I used Disk Cleanup to remove the Windows.old folder and because Win 10 blocked other methods, I ended up factory resetting with Recovery disks and then restored with the system image I'd created before upgrading.
If the YT videos don't play or not very well, that would point to a problem with the Nvidia graphics.
There is a means of getting into Safe Mode from within Win 10 but I don't know if you can get it with Networking.
Do not use msconfig as I did because you don't get Networking with Safe Mode when done like that and for me, when I tried to go back into msconfig to change back to a normal boot - nothing came up when I typed msconfig and I had to use the Cmd Prompt (Admin) to enter c:\Windows\System32\msconfig.exe to get back.
If the YT videos or your games work okay in Safe Mode with Networking using the on board VGA, then that would be a clincher.
If the YT videos don't play in normal mode, go into IE - Tools - Internet options and under the Advanced tab check the box for the first item which is Use software rendering instead of GPU rendering.
I think it requires a reboot to effect and then retry the YTs.
Do you have the games installed on your computer or do you have to access them via the 'net ?