With version 0.4.4 the fullscreen kinda works again, although I'd prefer having it centered instead of hugging the left side of the screen. Kinda bummed I lost my progress, feels boring to go through everything again, but I understand that's the drawback of playing demos :-)
As far as 'idle' games go, I like it! Love the sound effects, the plink plunk is really satisfying, especially because the sounds differ per level. And although I get hooked on idle games sometimes, it always feels really 'idle', however, because you actually drop marbles yourself it feels less idle, so makes me a bit less feeling like I'm completely wasting my time ;-)
Edit: I do feel like the sound design of the 'Wood' stage could be more subtle, especially when comparing it to the 'Rainbow' and 'Snow' level.