A staring-contest fighter where if you blink, you are left vulnerable. Possibly the other controls are mapped to face movements as well, but not necessarily. You have to stay focused and react, while also making sure not to blink. The fighting would be simple, maybe just one button to attack and one button to defend.
A platformer entirely controlled by face movements, where you blink to jump. If the face recognition is good enough to do this, the environment would change very slightly every time you blink, so that you might not notice it at first, but over time the changes build up. Maybe different mouth movements control running speed, like smiling makes you run faster and frowning makes you stop.