Look at the backs of the characters in Avatar. They don't animate realistically. I.e. there aren't enough degrees of freedom in e.g. the shoulder blades, in the sub-surface muscle, and in the secondary motion of the fat.
When it first came out I was so focused on the environment (especially in a 3D theater) that I didn't even notice how bad the bodies and mouths looked.
I recently rewatched it and it does not hold up well. Hopefully when they come out with special anniversary editions in the future, they'll redo all of that with the latest technology.
Fully realistic nude humans are still a ways off.