Lets face it, controversiality sells. GTA: San Andreas probably shifted extra copies once the Hot Coffee mod was discovered and Manhunt probably sold more when it appeared in the news as it was though to be the cause of the death of a teenager who was stabbed, more copies were probably shifted through curiousity.
So screw content, graphics and gameplay. Lets invent a game designed to be as controversial as possible. Winner gets an E-Cookie. I'll start.
You play as Jesus, with a big chaingun. And you have to kill everyone in the Vatican for misinterpreting the Bible. And you get health by raping the dead corpses of the male bishops. Then you go and kill all the supporters of the other religions for being blasphemous. Then you kill and the black people in the world and endit all with a spliff.
I doubt any of you can top that.