Blitz is probably the simplest game ever devised and requires just one button.
Basically your plane is on an ever moving course from left to right on a static single screen backdrop. You have no actual control of the plane itself. Once the plane moves off the right of the screen, it reappears on the left, only a bit lower. What this means is that your plane is forever getting closer to the city below. So, to enable your plane to land safely you have to destroy the city by dropping bombs. Once you've destroyed the city, you can land safely. You refuel, celebrate and then move onto the next city to repeat the process. That's it.
Obviously, if you don't destroy the city, you will eventually crash into a building. Then it's game over.