When I first saw the preview a while ago, I did some research on it and came to the conclusion it was going to suck (for reasons other than the graphics). I don't remember specifics of what bothered me, but basically it looked like it was going to be a really crappy "interpretation" of Beowulf and that just didn't appeal to me. I just did a couple quick searches though and can't figure out where I got that opinion from.
As for the justification for the CG, the IMDB FAQ includes this:
"Why is the entire movie CG, not live-action or live action+CG?:
Computer-generated images allowed the director, Robert Zemeckis, far more freedom than live-action filming would permit. Zemeckis has already made an all-CG movie, The Polar Express (2004), and knows its benefits. For this film, they include:
- camera moves that would not otherwise be possible;
- greater control over the art direction;
- greater ability to convincingly age the main character, who must grow fifty years over the course of the story;
- keeping costs down;
- images that look especially good in 3-D processes, such as IMAX or Real D."
Form your own opinions.