What is it like to be a mafia crime lord? Judging from the film The Godfather, it involves ruthless business dealings behind closed doors, cigar smoke-enshrouded conferences with your consigliari, the pain of exchanging your own humanity for the good of the Family, suddenly losing your loved ones to a hail of bullets, sending out hitmen to do your wetwork, and only occasionally getting your own hands dirty.
Judging from The Godfather video game, it involves a one-man army systematically eradicating hundreds of rival gangsters to conquer every business in the city one block at a time.
The same goes for any other role explored through an action game-- what was it like being a soldier in WW2? You ran down streets killing dozens of nazis at a stretch, blowing up tanks, planes and bridges single-handedly while absorbing, and near-instantly recovering from, hundreds of gunshot wounds. What is it like being a New York police officer? You gun down dozens of heavily-armed criminals on an hourly basis (sometimes with the assistance of slow-mo abilities.) A secret agent? A ninja? A yakuza thug? A space marine? A refugee in an underwater utopia gone wrong? Hell, an MIT-educated nuclear physicist? They all frame the same hook: single-handedly destroy a constant stream of hostile cannon fodder through binary violent conflict. Be a force of nature that crushes his enemies by the truckload. Be an Übermensch, a being that has surpassed mere humanity.
There are generally two aspects of the player character that set it apart: The first is the very autonomy granted via the PC being controlled directly by the player, as opposed to the surrounding characters who all follow programmed behaviors within the gameworld. The PC is an extension of an external force, the human, while NPCs are extensions of the machine.
But the form of the second aspect is specific to each given game, and is a mechanic or set of mechanics that improves the player's chances of survival numerically-- a designed-in advantage that makes the player outright more powerful or hardier than his enemies. Sometimes this power is supported by the game's fiction and sometimes not, but regardless always functions to elevate the player character above his foes, allowing him to kill them off in droves. In Crysis, it's the super-advanced "nanosuit;" in Max Payne or F.E.A.R. it's the ability to engage slow-mo "bullet time;" in Half-Life it's the hazard suit; in The Darkness it's Jackie's demon shroud; in Gears of War it's the ability for the player to regenerate health and be revived by his teammates; in Halo it's Master Chief's recharging energy shield, and so on and so forth.
For most games it's the simple logical fallacy of the player being the only actor in the world capable of refilling his own health. Do you see enemies in any shooter or action game slugging down medkits or painkillers during a fight like the player is able to? Do enemies in the Half-Life universe ever use the med stations placed around the world? Why don't the enemies in Halo or Gears of War have recharging health like the player does? The closest I've seen is the enemies in BioShock running up and using health stations, but they still don't use portable medkits to recharge their health in the midst of battle the way the player does. This imbalance between the player's and enemies' abilities in most combat-based games is simply nonsense, but it gives the player the edge to survive, to rise above his enemies.
The need to cast the player as an Übermensch stems from these games' inability to make a clean break from their roots: the old-school arcade shooter. Let's look at Robotron 2084. In Robotron, the player is presented with a sequential set of rooms. Within each room are two general types of actors beside the player: hostile enemies, who wander around in set patterns, and innocent civilians, who also wander aimlessly. Enemies will attempt to kill both the player and the civlians; the player's goal is to touch ("save") the civilians before they can be destroyed by the enemies, and to clear all the enemies from the room in order to move on the to next. The player character's advantages, beside being an autonomous agent of the player, are the ability to rapidly fire projectiles in each of 8 directions, quicker and more nimble movement than his foes, and the ability to use extra lives to continue once killed. The fiction of the game explains the situation of the player facing a massive enemy force and having extraordinary powers this way:
Inspired by his never-ending quest for progress, in 2084 man perfects the Robotrons: a robot species so advanced that man is inferior to his own creation. Guided by their infallible logic, the Robotrons conclude: the human race is inefficient, and therefore must be destroyed. You are the last hope of mankind. Due to a genetic engineering error, you possess superhuman powers. Your mission is to stop the Robotrons, and save the last human family.
Single-player games have the potential to be something else. I don't want to be an inhuman, one-man army anymore. Games could instead couch the player as a normal person within a functional gameworld, an equal actor in parallel with all the other characters, an individual that isn't tied to a progression of power from pistol to machine gun to rocket launcher. When I say I want a "GTA with gravity," I necessarily want to play a truly human character. Not a superbeing that can instantly refill their life bar at will, or respawn, unscathed, at a hospital when they die. Not a Man on a Mission to destroy the droves of hellspawn that have invaded the planet. Not an invincible killing machine with a nanosuit and slow-mo powers, or the result of a genetic engineering error. Just a person. Games need to find their humanity.