I've managed to get the installer to run, at last, but via a workaround.
I logged in as another non-root user and, in a console, su'd to the the different non-root user I use for gaming. Then, when I invoked the installer, it ran without the GTK interface, presumably because it didn't have the permissions it needed to use the current xorg session, and completed ok.
Logging back in as my gaming user I was able to run the updater, configure the settings and create a character. However, when I enter the game, it briefly displays my character, in what I assume is the starting location, for about 2-3 seconds, but then crashes.
I haven't found any obvious cause yet, but that's for another thread, in another section.