Is it sinful? My answer at the moment is, I'm not sure, and it's probably a matter of conscience. I don't know much about the games, so I'm sure I'm not the best judge of the matter. But I've heard that the premise is basically that you drive around and get points for hitting people, particularly police, children, and the elderly. That really doesn't sound like a "game" that a Christian should be playing. I think a big problem today is desensitization to evil acts because they are made so commonplace, and accepting them because they are made into jokes and games.Maybe a case can be made for, like you said, not following the main story (which I assume is the police officer killing type thing I mentioned earlier?) and just driving around, but then by buying the game you are supporting the game, and giving the makers money to do more of the same, not to mention from their perspective, you are making an approving "vote" of their game by buying it. Anyway, those are my thoughts, uninformed as they are.