Great animation
Animators love to hate mocap; they see it as taking their jobs. I know I'm going to offend some people here, and as a former animator I'm a little perturbed by this, but utilizing mocap in CoD4 was a great thing. The end result of mocapped motions can be awesome or it can be awful, and many animators love to point out the awful results as an argument against it. I'm afraid to report that our experience on CoD4 seals the case for us - the advantages of mocap in a photoreal game are huge.
We utilized the mocap team at Neversoft to capture the actions of actors, soldiers and stuntmen. Every shot was overseen by a lead animator, at least one game designer (generally the person who was responsible for the “vision” of that moment in the game), and a military expert (for authenticity). Everyone involved did a fantastic job, and the data we got back was much better than anything I've seen in the past.
I have to be clear about this though: mocap alone won't get you anywhere. In fact, thinking that mocap will replace animators is one guaranteed way to achieve the "awful" end result I mentioned earlier (even if you have good acting and direction).