Forgotten Worlds can be played by up to two players simultaneously. The player controls a flying muscle-bound soldier armed with a rifle with unlimited ammo. The Player 1 character is equipped with a long-range automatic rifle, while Player 2 has a short-range wide shot. The controls in the original coin-op version consists of an eight-way joystick for moving the character in the air while flying and a unique rotatable button known as the "roll switch".Rotating the switch left or right allows the player to adjust their character's aim in one of sixteen directions, while pressing it causes the player character to shoot his gun. This allows for the player to move their character anywhere while keeping their aim in one direction. Pressing the switch rapidly will cause the character to perform a "megacrush" attack will destroy all on-screen enemies, but at the expense of a portion of their vitality gauge.

The player character is accompanied by a satellite module orbiting near him that will provide backup firepower every time the player fires their gun. Like the main character, the satellite can also be rotated with the roll switch. Rotating the character while firing will only rotate the aim of the satellite, while rotating the character without firing will not only rotate the satellite's aim, it will also move its relative position around the player.

The player can obtain blue-colored coins known as "zennies" from defeating enemies throughout the game. The zennies are used as currency to obtain new power-up items from shops located at certain points in each stage. When the player enters an item shop, they are given a choice of the items available and a limited time to make any purchase they wish. These items consists primarily of new weapons for the satellite module, but also includes a health kit to restore lost vitality, an armor that allows the player to sustain additional damage, and even tips on how to defeat the boss awaiting at the end of the current stage.

Forgotten Worlds consists of five stages with a total of eight bosses. The player will lose if their vitality gauge runs out, but will be given a chance to continue.

Set in a distant future, an evil god known as Emperor Bios has destroyed most of the Earth, turning it into a desolated wasteland known as the "Dust World". Two nameless super-soldiers are created by the people to defeat Bios and the eight evil gods who serve him.