Metal Slug 4

Added bonus scoring system that allows the player to be rewarded depending on how many enemies were killed in the allotted time. The allotted time is determined by the type of emblem that is chosen. A time meter will appear at the top of the screen, and if the player resides to the end of the level, they will receive bonus points for badges that represent perfect feats. Eri and Tarma were replaced by Nadia and Trevor.

One year after the events of Metal Slug 3 , the world is trembling under a new threat of a mysterious but deadly cyber virus that threatens to attack and destroy the military computer system of any state. Tarma and Eri cannot help because of their own assignments in this matter, Marco and Fio are called upon to investigate the situation, to which the two newcomers Nadia and Trevor join. In their study, the group discovers that a rich terrorist organization, known as Amadeus (whose leader had previously appeared in the previous installments as a secondary witness who made treaties or trafficking with civilians and Morden soldiers), is behind the vile plot and united with the rebel army General Morden. They fight against the forces of Amadeus, hoping to destroy the cyber virus, until he destroyed the entire military computer system of the world.

Halfway through the game’s story mode, the player encounters someone they take to be General Morden. However, at the final stage, they find an underground object, where Morden-type androids are made and it turns out that the main characters throughout the game have destroyed the real General Morden. Allen O'Neill (who has repeatedly appeared throughout the series) is the last time he fights a player at this stage, and it turns out that he himself is a machine replicant. Finally, the player encounters the leader Amadeus, who uses large and powerful robots to destroy the main characters. However, he was defeated and fell into the trap of his own devices, since self-destruction was automatically activated and supposedly killed him. If the player safely escapes from the explosion of the base, then before the final captions will show that the team of heroes staged a victorious feast, but if the player falls into the explosion, the player’s character will appear in the hospital, which were delivered by Eri and Tarma. After the final credits, one computer monitor transmits data to an unknown place and turns off.

Metal Slug 4 received mixed reviews with positive results obtained by players with a user rating of 7.8 for PS2, 7.3 for Xbox, 8.1 for Neo Geo and 8.3 for arcade versions. While Metacritic and Gamrankings give estimates of 70.47% and 70 compilations with Metal Slug 5 for both the PS2 and Xbox ^{[1] [2] [3] [4] [5] [6] [7] [8 ] [9]} .