Idea's

1. Space invaders style game  
2. Astroids style game which you cant shoot, the point of the game is to dodge all the objects that approach you, every 5 seconds The objests speed double ,  and the object of the game is to keep dodging. 
3. Raceing game, where you have to tap a certain button which will move your character 1 unit towards the finish, the more rounds you get though the harder it becomes.