Started the upgrade about 10AM, all went well till near the final reboot to the login screen. Display froze though mouse still worked.
Let it sit for 45 minutes then dropped power and powered up. Went through same end of install then same hang.
Dropped it again. This time I started seeing flashes of the Desktop then back to the hang screen as above, flashing back and forth every few seconds.
Dropped power again and this time I get the desktop most of the time but it flashes back to the hung screen. Was able to click on Power then Shift click on Restart and rebooted to the repair screen.
Navigated through that till I was able to pick Rollback (Go back to previous build).
Looks like this is hung now, asll I see is a blue screen with Go back to previous build at the top and RUnning under it with the rotating circle of dots.
I'll give it a few ore minutes then nuke it and restore my image of 8.1.
Not happy with the upgrade process at all, even though I've already done it many times during the Insider Preview.
The biggest problem is there is no way to tell what is going on.
Can't Clean Install until after I can complete an upgrade install.