I didn't know that I was supposed to double back to the first door to end level one. I thought it was bugged, since I had all 10 notes and nothing happened. Each level just adds more features to the previous one, but I had a lot of fun with the enemy on levels 2 and 3. At first, I was convinced he was chasing me, but the more that I played I realized that he was actually patrolling. I couldn't use my cursor at the end, so I had to Alt+F4 out of the game, but it was a nice simple game.