Naturally. But that's a part of it. And of course, visuals can be key in telling a story, so they're not mutually exclusive.But that doesn't mean that science fiction or fantasy needs to be all about the visuals--if it were, what would we be doing with prose novels in the genre?
As for making hyperrealistic CGI human characters... Honestly, what would you get out of it that you couldn't get out of just filming a regular actor with a camera? We've had Napoleon, Julius Caesar, Adolf Hitler, and the others on film more times than I can count without a computer's help.
But now we could have them wholesale. This is perhaps most obvious for people of the media age - what if Anthony Hopkins had played Richard Nixon like Sam Worthington played a Na'vi?
Age comes in here too. Cameron has said in his next film with this tech, Battle Angel, will have an adult actress play a fourteen year old girl - maybe Sigourney Weaver could shave off a few decades off her age and do action roles again (we linger a bit on her avatar's introduction, and justly so - it's physicality is more than Weaver has had since, oh, the 1980s?).
Also, action movies. Who needs stunt doubles now, all manners of violence could be done without relying on snappy editing and the like.
Truly, anything goes. That is truly wondrous if this promise is realised. The fear, which is justified, that they'd feel odd or inhuman, the performances would look fake, I think has mostly been overcome by Avatar.
The money's needed to develop it, surely, but I am hopeful (as indicated) eventually people can make stuff like this in their basements. Imagine one actor doing several roles and each one looking different.But it shouldn't be used to do something that a person could do just as well--and for a bit less money!