Infinity Ward has a history of eliciting strong emotional responses in the games I've played. The ending of Call of Duty 4, in particular, as well as a few other moments from the game stick out in my mind. I think this opening scene is not just pandering to the lowest shock-value common denominator, but instead attempting to show firsthand what the player will be fighting to stop. It's really not significantly worse than your average action movie. With this scene, the player will be emotionally connected to the events that follow. After all, does anyone ever really get a sense of the scale of destruction they're trying to prevent in a game like this?