I just released an update to the game, which adds the following features:
- Background music for all levels
- Walking/sprinting noises for the player
- Customizable mouse sensitivity
- Better quit mechanics (now a label shows you how to quit when you press escape)
- An small hint on what you need to do for each level when you enter it
- Small fixes and changes here and there.
Thanks to Kai20 for the feedback and everyone that's played the game so far!