I don't see how this is groundbreaking, plenty of games kill off main characters and have done so long before Call Of Duty. More developed ones as well. The two main characters (Soap are Price) are fine. I suppose if you use the argument "we don't know if they are fine". Same thing with Halflife 2's endiing, which pre-dates it. The fellows who diesaren't so much characters as they are people who occasionally shout stuff. It also uses the age old cliche of the black guy getting it. It's pretty much an on-the-rails section while you watch a scripted sequence which Call Of Duty and other shooters have been using for a long time. Fairly archaic with gameplay usually suffering because of it.
I think probably Call Of Duty (1)'s Stalingrad missions do a better job of being effective in that regard as it's basically faceless scared Russians poorly equipped being led headfirst into a slaughter with officers shooting them if they turn back. Of course this isn't really clever or groundbreaking either as it's pretty much ripped off from enemy at the gates. Still it's a pretty cool sequence, I enjoyed that alot more than anything from the modern games.