Pong (Arcade, 1972)

Two rectangles playing tennis with a square ball.  The only colors are black and white.  The game is controlled with a single analog slider.  Pong (1972) is the game that has possibly the most historic significance for gaming.  It single-handedly popularized computer games for the mass public, propelled Atari into a market stronghold, and pioneered the video arcade.  It was not the first arcade game, however, and far from the first computer game.  Computer games have existed since the 1940's, when IT students used SONAR equipment and primitive computers to make the first games.  Space War was one of those early games, and Atari attempted to make that into an arcade cabinet before Pong, but it was a massive failure.  The control for Space War was too complicated, and audiences at the time could not get used to it.
In Space War, two players controlled separate ships trying to shoot at each other and avoid a black hole in the center, and used four buttons.  Two for rotation, one for forward thrust, and another to shoot.  It was a fairly clunky setup, even by today's standards.  Pong was more popular because it was a tennis simulation with simple controls.  Anyone could play and understand it.  The game was so popular that Atari was frequently called into vendors that housed it with complaints that the machine was broken.  Upon inspection, they found that the problem was that the chamber that held the quarters was stuffed.
There isn't much more you can talk about with Pong beside its historic significance.  The game is fun, sure, and it has held up well, but why would people play it today?  Why did people play it back then?  My theory is that being able to control what was happening on a screen was such a novelty that people could look past its simplicity.  In the 1890's, people would pay to watch a few second film strip called "Fred Ott's Sneeze," which is exactly what you saw.  Fred Ott sneezed.  The new technology could amaze people before they demanded stories, special effects and technical prowess.  Like the early films, the novelty of Pong was enough to make it a success.