Defender

Described as the hardest significant game of all time, this classic horizontal scrolling game has gained many fans.

The player flies a small spaceship above a long, mountainous landscape. The land is inhabited by a small number of humanoids. The landscape wraps around, so flying constantly in one direction will eventually bring the player back to their starting point. The player's ship can fly through the landscape without being harmed by it. The player is armed with a beam-like weapon which can be fired rapidly in a long horizontal line ahead of the spaceship, and also has a limited supply of smart bombs (three, to begin with), which can destroy every enemy on the screen.