Description taken from Arcade version of this game

In the year 2084 there is only one extended human family left, and it's your job to protect them from the merciless horde of robots who have taken over the world and would like to see them dead like their brethren.

There are five types of Robotrons to battle: Grunts, Brains, Enforcers, Tanks and Hulks. Each has its own strengths and weaknesses: Grunts are worth 100 points and attack in large numbers without shooting; Brains are worth 500 and shoot cruise missiles at you while turning humans into Progs; Enforcers fire guided mines, are worth 150 points, and are created by Spheroids which are worth 1000; Quarks are also worth 1000 and create Tanks, which will try to run you over or fire Bounce Bombs at you; Hulks can't be killed and can only be briefly halted by your blaster fire.

Three different types of family members must be saved: men in blue suits, women in pink dresses, and boys in red shirts. The humans are worth an increasing point value during each wave. They start at 1000 and climb to 5000, where they stay until the next wave or you're killed, at which point they reset to 1000. The goal on each screen is to grab as many humans as possible and kill all the Robotrons except for the indestructible Hulks. After board 255 the game starts over with the first screen again. ~ Brad Cook, All Game Guide