Soldier infiltrates a nuclear weapons facility to neutralize the terrorist
Soldier infiltrates a nuclear weapons facility to neutralize the terrorist
The player must navigate the protagonist, Solid Snake, through the game's areas without being detected by enemies. Detection is triggered by the player moving into an enemy's field of vision and sets off an alarm that draws armed enemies to his location
This also triggers "alert mode" and the player must then hide and remain undetected, at which point “evasion mode” begins and once the counter reaches zero the game returns to "infiltration mode" where enemies are not suspicious of Snake’s presence. The radar cannot be used in alert or evasion mode. In addition to the stealth gameplay, there are set piece sequences that entail firefights between the player and enemies.
To remain undetected, the player can perform techniques which make use of both Solid Snake's abilities and the environment, such as crawling under objects, using boxes as cover, ducking or hiding around walls, and making noise to distract enemies. An on-screen radar provides the player with location of nearby enemies and their field of vision. Snake can also make use of many items and gadgets, such as infra-red goggles and a cardboard box disguise. The emphasis on stealth promotes a less violent form of gameplay, as fights against large groups of enemies will often result in serious damage for the player.
Despite the switch to 3D, the game is still played primarily from an overhead perspective similar to the original 2D Metal Gear games. However, the camera angle will change during certain situations, such as a corner view when Snake flattens himself to a wall next to an open space, or into first-person when crawling under tight spaces or using certain items such as the binoculars or a sniper rifle. The player can also use the first-person view while remaining idle to look around Snake's surroundings or see what's ahead of him.
Progress is punctuated by cutscenes and codec, as well as encounters with bosses. To progress, players must discover the weaknesses of each boss and defeat them. Play controls and strategies can also be accessed via the Codec radio, where advice is delivered from Snake's support team; for example, the support team may chastise Snake for not saving his progress often enough, or explain his combat moves in terms of which buttons to press on the gamepad. The Codec is also used to provide exposition on the game's backstory.
Upon completion of the main story, a result screen is shown after the ending credits, which displays a statistics of the player's performance. The player is evaluated with a codename based on the number of alerts triggered, rations used and enemies killed throughout their playthrough, along with the total playtime, saves, and continues used after a game over. There are a total of 12 codenames for each difficulty level, with the best possible rank on the hardest setting being "Big Boss".