Well, if you look at Halo, there really isn't a good reason why it deserved the M rating. There was very little blood, almost no swearing, and no sexual themes, drugs, or alcohol. The reason it got an M rating was the Flood, and the only reason Halo ODST, Reach, and 4 are rated M is because they are Halo games. A T rating means that Bungie can make the exact same style of game, just without the dismemberment that occurred with the Flood. A game doesn't have to be overly bloody or vulgar to be great, Halo taught us that.