It'd be nice if there was a retry option on the level complete screen for those wanting to go for perfect scores instead of having to click "next level", then pause, then click "level select".
Or maybe, not have the star system at all? I mean, this game is all about trial and error to the point, that once you find the solution, it's trivial to go back and do it again perfectly. It's more like a judge if you somehow stumble on the right answer the first try. (Or watch someone else do it first.)