I'm aware this is a list thread, but it's in the wrong forum to start with games discussion is over there somewhere and it's a topic that particularly interests me from a discussion stand point.
I think a lot of people who haven't necessarily studied music or have but are limited to only enjoying the guitar miss just how important music is to setting and atmostphere... the best music is music that you don't even really notice, but is paramount to making the person in control, or watching (in the case of movies) feel a certain way.
I think the Call of Duty makers understand that, especially given that they used Hans Zimmer for the latest game.