The game is filled with cut scene "flashbacks" that reference what happened in previous Metal Gear Solid games and how the events or characters relate to the setting of MGS4. Players also have the choice of watching the Mission Briefings through set camera angles or freely exploring them with the Metal Gear Mk. II/III.
Snake is also partnered with a robotic drone, the Metal Gear Mk. II/III, which allows him to communicate with other characters, in addition to the CODEC radio system from previous games. It is also capable of incapacitating enemies using a weak electric shock, as well as providing reconnaissance. This drone is reminiscent of Gillian Seed's robotic sidekick of the same name from another Hideo Kojima game, Snatcher.
Snake's health plays a small factor during gameplay. If injured on the battlefield, cuts and burns will remain on his skin. However, the developers wished to avoid putting the stress of maintaining Snake's health onto the players, so he wears a muscle suit, allowing players to move in a similar fashion to previous games.
Snake has a meter and an index that replaces the stamina bar from Metal Gear Solid 3: Snake Eater. The index, "Stress," is based on current fighting and climate conditions. This can cause Snake to go into a "combat high," that sharply increases his accuracy and reduces damage taken. However, this effect will eventually wear off and could cause Snake to momentarily collapse. Smoking a cigarette calms him down. The meter, "Psyche," slowly drops over time reducing Snake's accuracy and his ability to recover his LIFE bar. Many items in the game – such as the iPod – will increase the meter, as will consuming ReGain Energy Drinks, noodles, and military rations, or using a compress on Snake's sore back muscles.
There is also a "Baseline Map" which is a radar map with a dynamic circle based on Snake's "presence" in regards to the environment
