It is on my must see list. Frank Miller has a real gritty gutsy style to his graphic novels, I really liked Sin City and this looks to be even bigger. A lot of green screen work here and they used XSI a lot, so yes a lot of CG work on this one. Of course if you are into Greek history, the whole story behind the 300 Spartans that defended against the whole Persian army is epic in scope alone.
http://300themovie.warnerbros.com/