The year is 2035, and its a zombie apocalpyse. You get bit and you have a choice, amputate the limb and wait for a cybernetic prosthetic, or become a zombie. Both have special benefits that I will list.
Cybernetic: Though you go through a portion of the game without an arm, the cybernetic limb can be given attachments and enhancements. Attachments include a grappling hook, grenade launcher, drill, and many others I don't care to list. Enhancements improve the melee or ranged damage you would do. An increase to strength would increase melee, a steady hand enhancement would improve accuracy. You can have a maximum of 5 enhancements and 2 attachments. Basically you would eriadicate the zombies to the best of your ability. Upgrades would cost money, and mini quests would be available. Like clearing a hospital full of zombies to retrieve medical supplies. Zombie: The disease isn't what you'd expect. As you eat certain humans, you regain sentient functions. Eating a former policeman or military person would give you the ability to use guns. As you become more sentient, you can choose to either stay with the zombies, or appeal to a group of zombies who see themselves better than the normal zombies as they too have gained all their senitient functions.