I like what Veret said. A lot of people misunderstand the concept of games "growing up." It's not about how much blood, gore, sex, and violence you can throw at a game (and don't get me wrong, I love my blood-splattered, gore-soaked, sexed-up, violent game as the next person). Rather it's about how you use the medium at hand to craft a story that fully utilizes that medium to convey a strong message, story, or emotional impact. Take Braid, for instance. Braid is one of my favorite games of all time. At first glance, it seems to be a unique side-scroller with an interesting time-manipulation mechanic. However, once the story starts to unfold and once you finish the game, you realize that each piece of the game (the level design, the time-manipulation, the art style) is used to it's fullest to create a bleak and somewhat depressing game with a very ambiguous ending. The game was fully utilized to craft this abstract story about time, loss, and (at least, from what I got) redemption. Braid is more grown up than most M-rated games out there. MW2 looks to be doing more of the same. Sure it's shooter, but IW doing all they can with the game to create a story that really hasn't been told in this way before and to invoke an emotional response from the player that a film really can't.