Contra 4

Contra 4 is based on the same 2D gameplay featured in the series through Contra III: The Alien Wars, ignoring many of the game mechanics introduced in later games, and returning to the old method of picking up power-up icons to obtain new weapons. The play controls are similar to Contra III, including the ability to hold two weapons in the player's inventory. The action spans both screens of the Nintendo DS system and a grappling hook can be used by the player's character to latch onto railings, allowing the player's character to move from one screen to the other. Similarly to the arcade version of Super Contra, the player can pick up the same power-up twice, giving them an improved version of the same weapon. The player can also discard a power-up, allowing them to try out a new weapon without losing a previous one.

In addition to the standard side view stages, there are also tunnel stages similar to the two "3D view" stages from the original Contra, in which the perspective shifts behind the character's back. The action in these stages is displayed solely on the upper screen, while the bottom screen is used to display the stage's map and the locations of power-ups. Other than using both screens, Contra 4 makes no usage of the DS' special features such as the touchscreen (besides navigating the main menu), microphone, or multiplayer modes.

The plot is set two years after the events of Contra III: The Alien Wars and three years before the events of Contra: Hard Corps. Following the defeat of Red Falcon, a new entity called "Black Viper" begins launching attacks against the human race. Bill Rizer and Lance Bean are joined by Mad Dog and Scorpion as they travel to the fictional Galuga archipelago near New Zealand (the setting of the original arcade version of Contra) on a "final" strike mission.

The game's producers took a number of liberties with the established canon. In the North American versions, Black Viper was originally the name of the main antagonist in Operation C, while "Mad Dog" and "Scorpion" were the codenames of Bill and Lance.

The DS version received "favorable" reviews according to the review aggregation website Metacritic. In Japan, Famitsu gave it a score of all four sevens for a total of 28 out of 40.

The game was hailed as a "rebirth" of the franchise, and was praised for returning to its roots. GameZone gave the game 8.9 out of 10, saying, "Contra 4 presents some of the best, most hardcore run-and-gun shooting action on the DS, and is a breath of fresh, alien-blood-scented air for the system, and gaming in general." However, Edge gave it six out of ten, saying, "Is there any need, on vertically scrolling levels, for your character to die when they touch the bottom of the screen, despite the fact you know there are platforms there? Do bosses have to seem impossible, and then prove tedious when their patterns have been learned?"