OOOOOH I get it now!! The first time I played it I didn't understand what to do, I just collected all the cubes and the time would run out and got 0 score. then I read the instructions.
It's always better for games to be clear by themselves. Maybe once you collected the cubes you'd highlight the main platform, or make it glow or something so it's clear you have to go back.
Next step would be to add personality and environment, nobody wants to play as a cube, maybe something memorable, like a platypus or a frog and for them to be on a forest or on a swamp. There are hundreds of free environment assets available everywhere. And maybe for it to be random every play (though I think it it should stay like this for the whole duration of the playthrough since ghosts should jump to the same places)
Other than that, interesting idea, feels like a solid tech demo and a good base to build upon, it gets really hard very quickly since at a certain point it's hard to dodge all black ghosts, so maybe a powerup to delete some ghosts or cap them? There are a few things that can be polished about mouse sensitivity and camera, but overall a decent entry with a promising future, good job!