I enjoyed playing the game, i reached level 10.. I think is a great game to have a little bit of relax when you don't have nothing to do.. If the game was mine I would add :
-other color stars that disapper after a while (but when catched give you x2 points)
-other (maybe black stars? ) to avoid cause they cause the lost of some stars
-maybe I would add falling from the top if you are not fast enough
-I would add a system that punish you if you did not collect the stars in a certain amount of time (like slowly level decrease)
-spending stars (even for different balls, different backgrounds);
-a reason for levelling up (like a costant that increase with the level that make points goes up)..
Btw I had fun playing it! It has potential to become a good smartphone game!