Metal Gear Solid: Peace Walker

Peace Walker consists of two primary gameplay modes: "Mission" and "Mother Base". "Mission" are the actual action sequences of the game, where the player must infiltrate an enemy territory or fight a boss, whereas "Mother Base" is an army management mode similar to the briefing screen in Portable Ops.

Players get to choose which missions to play from the "Mission Selector" screen. There are two main types of Missions: Main Ops are the primary story-based missions in which goals are determined by the narrative and must be played in a strict order in order to proceed. Some Main Ops missions include illustrated cutscenes that involve bits of interactivity in order to proceed. Extra Ops are optional missions that involve much more elaborate goals ranging from simple target practices to obtaining secret documents.

Peace Walker begins on November 4, 1974. Big Boss is running his own mercenary unit in Colombia after leaving the United States, following the death of The Boss during Operation Snake Eater ten years prior.

A mysterious paramilitary group equipped with a startling quantity of quality weapons, called the "Peace Sentinels", has been deployed in Costa Rica. Despite the Sentinels being equipped with firepower equivalent to that of a land army, the Costa Rican government cannot do anything about them because the country's constitution does not allow the creation of an official military. The Sentinels' presence threatens to endanger the balance of power between the East and West.

The idea of Peace Walker originated during the development of Metal Gear Solid: Portable Ops. Although Kojima planned to leave the project in the hands of other members from Kojima Productions, in order to make the plot's message clearer for the young demographic, he took the role of director at the same time as he was developing Metal Gear Solid 4: Guns of the Patriots. The game was made for the PlayStation Portable due to content that could only work on it, such as the cooperative multiplayer feature. While being a stealth-based game like the previous titles, new gameplay features such as the customization and levelling up were added to increase the replay value.

The use of a cooperative mode is intended to have players help each other and grow a sense of friendship. The development team that worked on Peace Walker was as large as the team that worked on Metal Gear Solid 4: Guns of the Patriots. Although several of the staff members had already worked on Metal Gear Solid: Portable Ops, Peace Walker was created with a different mindset. Kojima considered Peace Walker to be the biggest game he has ever worked on.

On Metacritic, the game holds a score of 89, indicating "generally favorable reviews". It was given a perfect score of 40/40 in the May 5, 2010 issue of Japanese magazine Weekly Famitsu; making it the fourteenth game to achieve a perfect score, as well as the first title for the PSP. PSM3 awarded the game 91%, commenting on the game's ability to "take the best bits from every Metal Gear Solid game – the recruitment tricks ... from Portable Ops, the camouflage and multi-player from MGS3: Snake Eater, the stripped-down controls from Metal Gear Solid 4 and the bonus missions ...

from VR Missions". 5/10, stating that it "is probably the biggest game in the Metal Gear series, and it's only on Sony's smallest system".