event viewer and dsim.exe are your friends (from an elevated command prompt of course)
I did exactly this, to no avail. And the DISM and SFC programs ran to 100% with no complaint.
As I said, the update did a full download, said it was installing, and crashed at the point of first shutdown and restart, when I took the least invasive “save personal information and apps” option.
When I took the next step, specifying “save personal info” (but not apps) setting, it looked as if the entire upgrade worked. I was able to start the computer in the new Windows 10 1703 version. But none of my drivers worked—Device Manager reported that my ethernet and wireless drivers were present, but that they could not be loaded. That meant I had a pretty brick. If I couldn’t go to the internet for update files (or anything else) the new system was useless.
Fortunately, the rollback option worked perfectly.