You are responsible for defending the Earth against an army of alien invaders. The task is not easy.
The attackers relentlessly descend toward the Earth as they fire their missile salvos in an attempt to destroy you. Alien Invasion is an obvious illegal clone of arcade hit Space Invaders from Taito (1978). It is apparently the first adaptation of Space Invaders on a home video game system. And not a bad one considering the system possibilities and the early date.
This version offers some interesting variations from the Arcade version: the 10 options let you specify the number of alien missiles fired at the same time (2 or 4), the number of missiles fired at the same time by the players (1 or 2) and number of players (1 player, 2 players alternate, 2 players cooperative). This last mode, 2 players playing at the same time, is quite innovtaive.