By bringing Sméagol and Gollum to live in Lord of the Rings, actor Andy Serkis set off a hailstorm of controversy. His proformance was so good that many Academy members felt he should be nominated for an Oscar (the Academy felt otherwise). He is able to inject great humanity into his motion capture work. Heavenly Sword marks the first time that Serkis has done motion-capture for a game. What's the difference between doing motion-capture and doing traditional acting?
The main thing is that there's really no difference between acting and motion-capturing. The research, the trying to embody a character is the same. But the main thing about motion-capture is that you're sort of puppeteering a version of yourself. You can calibrate that by manipulating certain things about your personality...I'm slightly ambivalent about the difference between playing a character and being motion-captured. It's no different from being in costume, except that instead of having synthetic materials on your face you've been captured in a game. Simple as that.