It is a comic book writ large.
While I've seen that, and many similar words written to disparage the movie, I think it's worth noting that widespread literacy in western civilization is a relatively recent development, and until post-Gutenberg era, our culture's mythology, legends and ideals were communicated through didactic imagery in icons, stained glass, statuary, painting and manuscripts illustrated not only to augment the written word but to instruct those incapable of reading them. Comic books (or 'graphic novels' if you prefer) are heirs to this tradition, and in many ways, I think 300 brings the transmission of our cultural legends around full circle...a real event mythologized, and communicated through the latest incarnation of the original means of transmitting such.