This game was quite challenging. However, some jumps felt a little too tight and were extremely hard to avoid popping the balloon. Additionally, you should consider letting the player control the balloon to some extent. My initial thought about the string was "I wonder if I can make it shorter". Also, consider adding a bit of story to the game. It would help make it more engaging. It doesn't have to be some big over arching story, just something to give a reason to be this robot with a balloon. But, I think expanding on this is definitely worth the time. It was quite satisfying finally getting to the end.