@adambegood

Well, I have to look at it a bit better.
And I have to install it all again, because I am working already a month on a new install.
So it can take a while.
But indeed looks pretty improved. :-)

Oh, I forgot to mention...

To play ColecoVision with blueMSX core you'll also have to get the BIOS, as pointed out in the docs: https://retropie.org.uk/docs/Colecovision/#lr-bluemsx-bios

I've updated the OP with this info.

(I've also tried installing Quasi88, which seems to have gone fine, but attempting to boot a game disk just leaves me looking at a black screen saying "V2 4MHz". I can access the menus with F12, but nothing in them gets me anywhere.)

EDIT: Ah, wait - so far as Quasi88 goes, it seems I was just really unlucky in my choice of games. I managed to pick a 100% fail rate of ones it doesn't seem to run (eg Xevious and Pac-Man). Other stuff like 1942, Bomb Jack and Dig Dug all work. They still don't in AdvMESS, though.

Added Atari 800, SNES, and Super Famicom.