After the nice title screen it was sadly rather unfinished...
For some reason going full-screen in my browser didn't work. The Archive tagged as a Linux version actually contains the WebGL files...I looked again, I missed that the archive lacked a top-level folder and the program to start was actually mixed into the folder I was in when I unzipped it. Fortunately I made a subfolder for the game beforehand since I downloaded the build and the source and extracted the source archive already.
Anyway, I took the source project and built my own copy of it...