this article from The Guardian film blog on the upcoming Tintin feature makes a strong case for motion capture + cgi, at least in the context of comic book adaptations ..
“..With comic-book adaptations in particular, dialogue that appears charmingly brazen on the printed page can become hokey on the big screen, especially when mouthed by an actor whose face we probably know more intricately than those of most of our own friends. It’s why Superman is always played by a virtual unknown. If he’d been portrayed by Nicolas Cage, as was once posited, no one would have been able to suspend disbelief. But put Nicolas Cage in a motion capture studio and the world might easily believe him as the Man of Steel in an animated take. Animation may just offer us a half-way house: we get to enjoy great actors without having to ignore the fact that they are real people. It’s a brand new tool, one which dramatically obviates the requirement for us to use our imagination to mentally touch up a given moving image…”