08-03-2018, 03:29 PM
A complete removal, a reinstall, a complete removal and a totally different windoze installer later and I'm in business.
I did a most thorough removal of the install: The installer left behind the entire directory structure, a few other files and registry entries, so those were manually removed.
Reinstalled it and encountered the same problems. Rinse and repeat!
Somewhere, someone mentioned success using a different installer,
so after cleaning up again, I tried a different installer on a different GIMP mirror. 
Now GIMP 2.10 works as it should. And, <<bonus>> there is also useful error output.
I did a most thorough removal of the install: The installer left behind the entire directory structure, a few other files and registry entries, so those were manually removed.
Reinstalled it and encountered the same problems. Rinse and repeat!
Somewhere, someone mentioned success using a different installer,
so after cleaning up again, I tried a different installer on a different GIMP mirror. Now GIMP 2.10 works as it should. And, <<bonus>> there is also useful error output.