Unlike the other previous titles on PSP, Metal Gear Acid and its sequel, which were turn-based tactical games with stealth elements, MPO retains the action-based gameplay from the console iterations, drawing heavily from Snake Eater and utilizing the camera system from Subsistence.
The main addition to MPO is the Comrade redical System. Instead of the solo missions that the series is known for, MPO goes for a squad-based approach, with Snake having to recruit allies and form a team of trained specialists. Before each mission, the player must compose a four-man squad. The squad is then sent into battle. Each member of Snake's squad has their own strengths and weaknesses. While some uni
ts are best utilized on the battlefield, others may specialize in producing items, healing allies, or providing intel for each of the game's maps.Characters who are killed in combat are eliminated from the player's squad permanently, unless they are special characters, such as Snake. Special characters also include team mates that are bosses or supporting characters in the story. If a special character's health is reduced to zero, they are sent to the infirmary, in order to recover. The player can also abort the mission.
Another new feature is the surround indicator added to the game's HUD. Similar to the radar in previous titles, the surround indicator allows players to determine the relative proximity of enemy soldiers by the noises they make. The surround indicator is composed of two circles; the outer circle displays t
he noises made by enemies and inner circle displays noises made by the player himself.The game also contains a Wi-Fi-enabled multiplayer mode, which is an expansion of the Metal Gear Online mode previously featured in Subsistence. One's performance in the Online Mode may affect their performance in the single player campaign; the player can recruit and trade soldiers from beaten opponents, or vice-versa. Additionally, certain multiplayer options result in recruits being removed from the one's single player roster permanently. In contrast to the console games in the series, the cutscenes that drive the story are not rendered using the usual in-game engine. Instead, they are presented using an animated comic style comprised of hand-drawn artwork by artist Ashley Wood.
The game also features voice acting, consisting of returning cast members from Snake Eater and new actors. However, the number of cutscenes and in-game voiced sections are minimal, due to the PSP's UMD storage capacity constraints.
