Crackdown is one of my favorite games I have played.
To start off, this is not a GTA style game! It is a sandbox game. There are major differences between GTA and Crackdown.
In Crackdown you are a police, cleaning up the city from the gangs. You don't really hear any curse words, and the killing isn't bad. There is little blood, and the characters are in a slight cartoonish look. No sexual stuff in the game and you don't really hijack cars much, because you can basically run just as fast, if not sometimes faster than the cars.
I really think this game deserves a Teen rating, but the reason why it got the M rating is because T ratings aren't strict on age, so it still means a 6 year old could play this game and buy it if he wanted. But this game is fine for 12 and up I think. Like I said, just because it has the M rating and says GTA style, it is not like GTA AT ALL. There is so much more to GTA, and you can't say 2 games are a like just because of 1 thing you can do that is the same (steal cars) but even in that case, you are a police, and can confiscate vehicles in theory. And you get demoted by killing civilians. The auto lock on doesn't even lock on to civilians either.
Just my opinions.