I love this game.
The challenges were a great add-on, because it makes the game more complicated. The set ball sizes balance out the difficulty of the entire game. Overall, this was a lot of fun.
However, regarding the level editor, it would be a lot easier if you installed an IMPORT option so further level editing could be done. Also in some cases, the ball may pass through a block if it's going too fast.
Regardless, this was amazing. I hope you can fix these problems!