Sega‘s Zaxxon is an early arcade shooter that broke the mould. It was first released in 1982.
Zaxxon was unique (at the time) because it was one of the first ever video games to use an isometric point of view for the graphics and action.
You fly a (non-stopping) spaceship, through a Star Wars-like trench, blasting gun turrents and fuel dumps, in order to make it to the end of level boss. The isometric viewpoint, and the shadow of your ship, allow you to judge where you are on the X and Y axes, and you can move left and right and up and down in response to oncoming obstacles.
Zaxxon is a very short game, but extremely condensed with action. Two fortress levels, an adjoining space level, and a boss fight (Zaxxon himself – another first, for boss battles of this nature). If you know what you’re doing, and have luck on your side, you can probably beat the game is less than 15 minutes. The going is torturously difficult though.
Zaxxon had a huge influence on other game-makers. Virtually every budding coder back in 1984 was trying to make their own version of it. In BASIC… Zaxxon popularised a now common video game viewpoint – “isometricalism” I’m calling it… Zaxxon even beat Knight Lore and Ant Attack to the idea, and it was all Sega‘s doing. With their first ever game… Not bad, eh?
A sequel, called Super Zaxxon, was released the following year.
More: Zaxxon on Wikipedia