I hate Modern Warfare as much as the next guy, but I think that people are seriously overreacting. The ad is extremely clear about what is actually going on, that this is all taking place in some sort of game space. The noob actually is blown up and respawns (which he treats as a mild inconvenience,) they make an in joke about how overpowered knives were in MW2, and the two are acting completely ridiculous the whole time. The creators of the commercial went to great lengths so it would be as obvious as possible that this is not even pretending to be real. Furthermore, It does not depict or trivialize any real world events or individuals. This advertisement is completely removed from the idea of actual war.
The claim that this is offensive because it takes place in real places and is live action has some merit, but only if we are willing to level the same criticism to 80% of all action movies and TV shows made in the last 50 years. For example, The A Team reboot was live action, took place in real places, and depicted people having fun making war and killing people. The exact same reasons this advertisement is being condemned.
A little tasteless? Maybe. A new low? Hardly.