noblemonkey: I've not heard back from support yet, but here is something I tried and it _seems_ to have worked.
I opened GoG Galaxy and then very quickly before it could run the update for the gaeme, I turned off auto-updates for the game only.
I then closed GoG Galaxy and re-opened it. Then I went to the game and pressed the "Verify / Repair" option and it then downloaded the ~300MB patch others have mentioned.
It installed and is now working.
Weird.
I was having the 92% installation error, so i use the offline installer, it worked and the game installed, but GOG keep trying to update and failing, so i did this, open GOG, went to the game, click on the options icon, the one next to PLAY, > Manage installation > Config > disable auto update, click ok and close and reopen GOG, went to the game one more time and click on the options icon, the one next to PLAY, > Manage installation > Verify / Repair, then downloaded a 336 MB update, it fix everything, i turn on auto updates and its perfect.
To access the offline installation go to:
https://www.gog.com/account click on the game and them DOWNLOAD OFFLINE BACKUP GAME INSTALLERS.