Hi, I would say that what we have here now is just testing out what you can do with construct2, so I can't really say much at this point, your game just doesn't have much content yet, but after you change couple of things and add this and that, this game could become enjoyable to play.
I will list some things you could improve.
Controls are a bit weird, it would be better if you could just keep button pressed down, now you have to keep hitting them.
Game screen is so high it doesn't fit on my 800px high sreen.
you could add function that you can't finish the level before you have collected all yellow balls.
you could also add different things on levels, now just position of yellow balls is different.