In Guns of the Patriots, players assume the role of an aged Solid Snake (colloquially referred to as Old Snake), using stealth, close-quarters combat, and traditional Metal Gear combat. The overhead third-person view camera of earlier games has been replaced by a streamlined view and over-the-shoulder camera for aiming a weapon, with an optional first-person view like a first-person shooter at the toggle of a button.
A further addition to gameplay mechanics is the Psyche Meter. Psyche is decreased by non-lethal attacks and is influenced by battlefield psychology. Stressors (including temperature extremes, foul smells, and being hunted by the enemy) increase Snake's stress gauge, eventually depleting his Psyche. Adverse effects include difficulty in aiming, more frequent back pain and the possibility of Snake passing out upon receiving damage. If Snake kills too many enemies in a short amount of time, he will have a vision of Liquid and vomit, greatly reducing his Psyche. Among the available methods of restoring Psyche are eating, drinking, smoking, and reading an adult magazine.[4]
Snake has a few gadgets to aid him in battle. The OctoCamo suit mimics the appearance and texture of any surface in a similar fashion to an octopus, decreasing the probability of Snake being noticed. Additionally, FaceCamo is made available to players after they defeat Laughing Octopus. FaceCamo can be worn by Solid Snake on his face and it can be set to either work in tandem with the Octocamo or instead mimic the face of other in-game characters. To get access to these unique FaceCamos, players have to complete certain in-game requirements first. When the FaceCamo is worn with OctoCamo, under ideal conditions, Snake's stealth quotient can reach 100%. The Solid Eye device highlights items and enemies and can operate in a night vision and a binocular mode. It also offers a baseline map, which indicates the location of nearby units.[5] The latter function is also performed by the Threat Ring, a visualization of Snake's senses that deforms based on nearby unit proximity and relays them to the player.