The gameplay mechanics are the same as in previous Metal Slug games; the player must shoot constantly at a continual stream of enemies in order to reach the end of each level.

Several years ago, the evil General Morden was foiled in his attempted coup d'état against the worlds' governments by the Peregrine Falcon Strike Force.

After forming an alliance with an alien race in an attempt to stage another coup, Morden was betrayed and taken prisoner by his newfound allies.

His rebels troops formed an ad hoc alliance with the Strike Force and the aliens were defeated and Morden was killed.

Rossi (now a Major) and Roving (now a Captain) led the fight against the Morden during the second coup, joined by two members of the Intelligence Agency's Special Ops Squad S.P.A.R.R.O.W.S.

Determined to wipe out every remnant of Morden's powerbase, the army send Rossi and Roving to destroy all remaining rebel strongholds, one by one.

come across a series of strange events which lead the army to conclude that the aliens with whom Morden once allied himself have returned.

After destroying the ship's core, the Strike Force must fight their way through armies of clones of their captured teammate, some of whom have turned into zombies.

A battle ensues in Earth's atmosphere, which is won by the Strike Force, who leave Rootmars' body in the ocean.

In the PlayStation 2 (PS2) and Xbox versions of the game, once the arcade mode has been beaten, there are two additional mini-games: "Storming the UFO Mothership" and "Fat Island".

In "Fat Island", two players compete to gain the most weight in a limited amount of time by eating various foods.

The game features upscaled graphics and co-op online gameplay, but it does not include the extra modes from console releases.

[15] He scored the Xbox 360 version 7.4 out of 10, again feeling that the game was good for what it was, but somewhat dated when compared to other titles: "Before you purchase Metal Slug 3, you need to ask yourself how much you value ten dollars.

Of the Xbox version, he praised most aspects of the game, but criticized the excessive difficulty: "The fundamentals of Metal Slug 3 are all really excellent.

You'll be hard-pressed to find another 2D side-scroller with such detailed environments and smooth animation, and the gameplay is the dictionary definition of frenetic.

You can try and collect all the extras (Japanese radish and Chinese cabbage are all there for the taking), but there's no getting away from the fact that there's not enough in here to warrant shelling out full whack, no matter how perfect a slice of arcade action it may be".

[23] Patrick Garratt were more impressed with the Xbox 360 version, which he scored 9 out of 10, writing: "What's really fascinating here is the fact that a vaguely ageing title appears to have found its niche market on a modern console - this is Metal Slug 3's ideal home, and you'd be a fool not to make it welcome in yours".

[24] GameSpy's Darryl Vassar scored the Xbox version 4 out of 5, arguing that "while each of the individual parts of Metal Slug 3 are unremarkable, they come together in a way that is greater than their sum.