In this demo paper, we present a shoot'em up game similar to Space Invaders called the "Mood Game" that incorporates players' affective state into the game mechanics in order to enhance the gaming experience and avoid undesired emotions like frustration and boredom. By tracking emotions through facial expressions combined with self-evaluation, keystrokes and performance measures, we have developed a game logic that adapts the playing difficulty based on the player's emotional state. The implemented algorithm automatically adjusts the enemy spawn rate and enemy behavior, the amount of obstacles, the number and type of power ups and the game speed to provide a smooth game play for different player skills. The effects of our dynamic game balancing mechanism will be tested in future work.