Very interesting game! I managed to get 203, 213 and finally 280 points at the end. I think there could be different goals, they even may be chosen randomly when you start the game.
The first goal would be to get minimum point (means, to perform minimal number of shoots). The second goal - is to complete a game for a minimal time. The main and third goal could be in opposite - to reach maximum points. Makes sense because more balls make harder to complete a level.
Also as an idea - there could be different background music when you reach new levels.
Overall it's an interesting game with a potential. Great job!