OK... Does an M rating define the game as mature? Absofrikkinlutely not. I'd like to use two games as examples. First, Project OVERKILL!! for the PSX was rated M, although spend 5 minutes playing that game and you'd realize it to be one of the most immature games you ever played. All that game had to offer, at all, was "Buckets of blood."
Another game on the PSX was IQube (rated E). A simple puzzle game with moderate graphics (for its time), which contained no language, sex, or violence (unless you call room sized bricks toppling over a guy violence), yet it was much more mature than "Buckets of blood".
You see boys and girls, violence, language, and sex don't define a game as mature. It is the theme that determines a game as mature. Jacking cars and shooting cops doesn't make the game mature, it is the lower-mid 90s LA gang life story that made the game mature. That is something a kid wouldn't get, so they'd just shoot cops and laugh, even though that isn't the premise of the game. Violence, language, and sex only serve to enrich and reinforce what is already there. On the same hand, if it's censored out, it's not believeable.