I'm using Windows 10... it seems that despite trying to get the newest version of Java I ended up with version 8... maybe Windows' fault due to its version? I don't know. I'll try and find time to troubleshoot (more uninstalls probably) but it looks like the problem is squarely at my end (the error message given said it could only run packages up to version 52 but this game was packaged with version 55).
Apologies for the trouble.