uncharted 4 writer Josh Scherr has elaborated on the huge graphical leap forward the PS4 has offered him and his team.
We’ve completely revamped our facial animation systems," he explained. "The previous Uncharted games, and in The Last Of Us, the characters all had about 90 to 100 ‘bones’ in their faces which we used to move the meshes around.
"Think about that, about how detailed Joel and Ellie’s pained facial expressions were, how well the game captured the respective actors’ – Troy Baker and Ashley Johnson – seminal roles. All that was achieved on the old tech. Now, the faces have anywhere between 300 and 500 bones.”
http://www.ign.com/articles/2015/05/13/uncharted-4-faces-up-to-5-times-more-expressive-than-the-last-of-us