It was cool to realize the abilities of combined balls, but I agree with @Edgor when they say that a bit of explanation (or feedback to let us know that we're progressing... I'm still not sure if the levels were just infinitely randomly generated) may have helped.
I agree with the rest as well - the only thing your game is missing to be really close to an idea that you can run with is a few other interactables, which would in turn spawn specific levels and thus a bit of progressive structure (or randomly spawning levels, whatever you'd want)... and maybe a soundtrack that's a bit less stressful. XD
Nice concept!