I really liked the art, and also the gameplay! I also love that when you lose, there is no death animation or anything. The timer just resets. This (in my opinion) gives the game a more polished and smooth feeling.
Great job.
EDIT: NEVERMIND this is actually a 10/10. The hidden world and the secret ending? That's amazing! I'm giving everything 5 stars now, this deserves to win.