Yes, it is a hard game. Congratulations on that. But it's also not very inviting to play, if the only medal you're giving away is available only for perfect play. You offer difficulty related stars in game, why not medals? It keeps the players attached to your game. Progress will be shown through some achievement.
Aside from that, in some levels you depend on a very tiny spot to fit through. On some occasions you might not fall the same way twice so you get stuck between to blocks which had let you pass every other time. This I don't consider hard but buggy.