The original arcade version of Donkey Kong had many things not familiar in arcade games at the time. There were recognizable characters with recognizeable traits, not just spaceships or abstract aliens. There was a story that developed as the game progressed. Most impressive of all, there were four entirely different screens, opening the playfield wider than it ever had been before.
For those reasons, and certainly also because of the addictive game play, Donkey Kong is a landmark in video game history.