From HappyBay Mobi:
The player (1 is Marco and 2 is Tarma) has to constantly shoot at a continual stream of enemies in order to reach the end of a level. At the end of each level, the player confronts a boss who is often considerably larger than regular enemies and takes many shots to defeat. On the way through the level, the player finds weapons upgrades and "Metal Slug" tanks, known as the SV-001 (Super Vehicle), that can be used not only as weapons but also as added defense. The protagonists can perform melee attacks by using a knife and/or kicking. The player does not die for simply coming into contact with most enemies. Correspondingly, many of the enemy troops have melee attacks. Much of the game's scenery is destructible. Sometimes this reveals extra items or powerups, most of the time it simply results in collateral damage. During the course of a level, the player encounters prisoners of war. If they are freed, the player can receive bonuses in the form of random items or weapons. The player receives a score bonus for freeing POWs at the end of the level; at this point the game shows the name and rank for each of the prisoners freed. If the player dies before the end of the level, the tally of freed POWs is restarted. There are a total of six levels, with themes ranging from forests, garrisoned cities, snowy mountain valleys, canyons, and military bases.