Andy Serkis, the actor behind Gollum and a star of the new Tintin movie, rubbishes the distinction between motion-capture performances and "real" acting:
[T]he acting part of the process is entirely the same. I've been bombarded by hate mail from animators saying, "How dare you talk about 'your' character when all these people work on it after the fact? We're actors as well." They are actors in the sense that they create key frames and the computer will join up the dots, carefully choreograph a moment or an expression and accent it with an emotion. But that's not what an actor does. An actor finds things in the moment with a director and other actors that you don't have time to hand-draw or animate with a computer.
Alyssa Rosenberg complicates the claim:
[T]here’s a difference between technological alteration without which a performance could not exist, and post-production work that tweaks or modifies a performance or a set but that does not constitute the core of the work. Our current awards categories don’t provide appropriate recognition to the first category of technological and post-production work. I want Serkis to get piles of statues. I just think we have to find a way to acknowledge the interactive nature of the work.
The Dish 