One button, one track, and a world that comes at you until it wins.
Take a platformer and remove the choice of where to go. The world scrolls at you by itself, you have one button, and there is no last level: it only gets faster until you miss. What is left is the purest reaction test in games, which is why it is the style phones took over.
Games like this: Flappy Bird, Geometry Dash, Subway Surfers.