Well, this was anti-climactic.
I decided I should finally start to play Torment - Tides of Numenera.
It's been a while, so I needed to update GOG Galaxy.
That finished, and I had to reinstall the game. So I did that, waiting for a long time as it downloaded and installed.
Then I didn't have any time to play, so I set this all aside and went off to finish my home work and then headed off to work.
I got home, and fired the game up and all I got was this:
"Switching to resolution 0x0 failed, trying lower one
Switching to resolution 0x0 failed, trying lower one
All resolution switches have failed
Screen: could not switch resolution (1366x768 fs=1 hz=0)"
So clearly I need to spend some time tinkering with my resolutions. The game ran once before, when I first got it, I just didn't feel like spending the time to play around much. Now it doesn't work at all. My enthusiasm was pretty much "I should play this, I paid for it" and that's not a good sustainable base for serious troubleshooting.