The game is pretty cool. The only thing I suggest is you add some background music. I do have to ask how to beat the fourth level though.
I chose not to include background music because I lack the skill to create music, and I did not want the background music to be just another generic, free track.
The fourth level introduces the player's ball ejection mechanic. However, it should only be ejected at a specific moment, when one of the entities is positioned in a specific location.