A simulation, but not the sims? I agree.
Make it a FPS, but you don't have to use a gun in the game. You can just be a regular guy, go to work....come home, go out for some drinks, get wasted, etc. OR.....you can turn into a psycho serial killer and sneak in your neighbors home a slit his throat. Or you can just be a burgler. Or maybe you go rob the convenience store. If EA makes the game you can practice sports, and then integrate the sports games if you get really good and become an NBA basketball player. But still keep the FPS style when not playing a game.
Then the NBA player gets done with a game and he is a serial killer at night.
"Do anything, Do Everything" I think that is the game of the future.
Also, have it be an online game (as well as single player). People in your neighborhood are other people playing the game. However, to prevent it from being a massive chaotic kill everyone game, have HUGE penalties for dying or getting arrested (for online only). Allow like 5 characters per account, for example, and have jail time range from a couple of days to a maximum of 3 - 6 months. Realistic risks for committing crimes would be genius, instead of respawning at the police station or hospital, i.e. GTA3.
If you die you either go to heaven or ****. Your life will be reviewed and if you go to heaven god may put your soul back on earth very shortly. If you are bad and go to ****, you get tortured for a couple of weeks before going back to earth. God may put your soul into a wealthy CEO and you have an awesome house with lots of cars, but if you are bad your soul is inserted in a garbageman's body.
With up to 5 characters allowed, you could have the safe characters (law-abiding) so you always will be able to play. A not so bad guy would be a vigilante type who only targets and kills bad guys, or maybe you get into the profession of being a police officer. Or a counter-terrorist, like CS.
This game is a long ways away from being possible, but I bet within 10 years we will have the hardware and software capabilities of creating a game like this.
Maybe in VR too.....