This game is so frustrating that at level 10 I just plain stopped caring. If you want to make a physics-based game like this that has limited shots, being able to control the strength of the shot precisely is a MUST, not a "nice to have." Shots have to be repeatable on future attempts.
If you don't change the controls I will not play this game again. Ever. The idea is great, and the physics work well enough, and the visual style is fantastic. But the controls are the deal breaker.
You either need to make the number of shots unlimited and have the star ranking be based on a combination of stars collected and shots used, or you need to give us precise strength control. Otherwise, for all intents and purposes, the game might as well be unplayable, and I have rated it as such.