A game i wish existed would be a game that simulated a larger city, that works completely independently of the player. With its seperate political, economic and such system.
With a bit of wackiness. Basically the player explores this city and does whatever he wishes to. Meanwhile things happen everywhere. Gangs fight each other, the police works on things.
And in the labs, scientists constantly conduct experiments. Every citizen would have a simulated psyche. So a scientist who has done nothing but researching the same bacteria for years would possibly go mad and unleash it upon the city.
By doing anything i mean anything, no exceptions, no exceptions to life either. You would have bodily functions(yeah piss and poo and stuff, and sex drive) that you would have to keep in mind.
You could do anything. Act as socipathic as you want, with the added consequence of getting murdered or arrested and having your character arrested for multiple ingame years.
If there could be multiplayer, it would be awesome. Trying to bring down the virtual soceity or controlling and opressing it with your own homemade robots! There would even be progress in time, like if you play long enough a foreign nations force could invade the city and replace its goverment, or a disease could wipe out people or turn them into zombies, or you could start a civil war by assasinating all administrators of the city. A corperation could get their shizzle together and unleash an opressive robot regime upon the game world. Anything, seriously.