Near the end of the 20th century, a small fortified nation named Outer Heaven (founded by a mysterious war hero who's name and useridentity are shrouded in secrecy) is threatening the nations of the "West" with the development of a new prototype weapon named Metal Gear, a walking tank which is capable of launching nuclear warheads from anywhere on the globe. As FOX-HOUND's (an elite black ops unit) newest recruit, going by the codename of Solid Snake, your mission is to infiltrate Outer Heaven and rescue your missing comrade, Grey Fox (who was captured after a failed infiltration), while gathering intelligence on Metal Gear. In order to fulfill your objective, you must collect various weapons and equipments (including keycards for further access into the fortress), while avoiding visual contact with the enemy. The player must also confront against bosses in the form of Outer Heaven's elite mercenary force and rescue hostages hidden within the fortress in order to increase their rank, which gives the player an extended life bar and increased storage capacity for replenishable items and ammo. The player can use a wireless transceiver to come in touch with their commanding officer, Big Boss, to learn more about their current mission objectives or contact one of the local resistance user operating covertly within the fortress to gain useful tips and insights.

Story:
A new Metal Gear prototype (codename Gander) has been stolen by a separatist guerrilla group in the region of Gindra in Central Africa. The group, known as the Gindra Liberation Front (or GLF), plans on using the prototype as a means of achieving victory in an ongoing civil war. Solid Snake, the FOXHOUND operative responsible for the destruction of the original Metal Gear seven years before, is brought back from his retirement in Alaska. His mission is to infiltrate the group's headquarters Galuade, the fortress that was formerly Outer Heaven.

Gameplay:
MGS follows the overhead 2D format previously used in the 1990 MSX2 game Metal Gear 2: Solid Snake while adding a few new elements introduced in the original Metal Gear Solid. As with previous games in the series, the objective is to infiltrate the enemy's stronghold while avoiding detection from guards or surveillance systems.

An unofficial sequel to the original Metal Gear for the NES. Three years has passed since the Outer Heaven incident. FOX-HOUND has gained intelligence that an unknown terrorist group has seized a remote facility containing mass-produced Metal Gear tanks, as well as a new Metal Gear prototype which was under development. The newly-promoted Lt. Solid Snake is called back into action to infiltrate the terrorists' base with the help of two FOX-HOUND rookies, former marine Nick Myer and navy intelligence agent John Turner.

The player once again assume the role of Snake. The objective is similar to the previous game, as the player must avoid any kind of visual contact (even moreso than the first game), while collecting weapons and equipment on-site. There is a greater variety of areas such as a jungle, a warehouse, a train, a couple of prisons and even a cargo ship containing the mass-produced Metal Gears. The player must also overcome new traps such as searchlights, soldiers in gyrocopters, door-sealing devices and even suicide bombers. The player must also interrogate captured enemy officers by injecting them with a truth serum to increase their rank, in addition to saving hostages like in the first game. Side-scrolling areas are also included in addition to the main overhead game, where the game takes a more action-oriented route (while still maintaining the stealth premise).