The player(s) must shoot constantly at a continual stream of enemies in order to reach the end of each level. At this point, the player confronts a boss, who is usually considerably larger and tougher than regular enemies. On the way through each level, the player can find numerous weapon upgrades and "Metal Slug" tanks. The tank is known as the SV-001 ("SV" stands for Super Vehicle), which not only increases the player's offense, but considerably adds to their defense.
In addition to shooting, the player can also perform melee attacks by using a knife. The player does not die simply by coming into contact with enemies, and correspondingly, many of the enemy troops also have melee attacks. Much of the game's scenery is also destructible, and occasionally, this reveals extra items or power-ups, although most of the time it simply results in collateral damage.
During the course of a level, the player also encounters POWs, who, if freed, offer the player bonuses in the form of random items or weapons. At the end of each level, the player receives a scoring bonus based on the number of freed POWs. If the player dies before the end of the level, the tally of freed POWs reverts to zero.
There are a total of six levels, in locations such as forests, garrisoned cities, snowy mountain valleys, canyons, and military bases. The vast majority of enemies are soldiers equipped with weaponry befitting their specific role. There are also several mechanized enemies, such as tanks, mobile artillery, aircraft, armored personnel carriers and technicals. Much of the game's humor comes from how the enemies are depicted; the player often encounters them as they are sunbathing, roasting food over a fire, or simply conversing amongst themselves. They also tend to scream loudly if they see the player, and often try to run away.
This article uses material from the Wikipedia article Metal Slug, https://en.wikipedia.org/wiki/Metal_Slug, which is released under the Creative Commons Attribution-Share-Alike License 3.0, https://creativecommons.org/licenses/by-sa/3.0/.