Visually, it's effectively done. Everything's processed with a surreal golden glow, adding warmth, and the gore - of which there is plenty - is stylised, too. I suspect that, as with Sin City, the look is very much influenced by the comic book. Take, for example, a flashback to fight between a young boy and a wolf - the wolf is more drawing than real. (But here there's an error: the narrator describes this beast with glow red eyes, why the animator's provided one whose eyes are yellow.)
The fight scenes are mostly good. Did the Spartans use phalanxes? I thought that was a Roman invention. Maybe I'm wrong. Still, it gave the impression of generally well-drilled soldiers who have considered their problems in battle scenarios, and devised strategies to address them. Occasionally, there are melees, which seem out of place with the disciplined approach, but the choreography's great: parry, mutilate, onward, with limbs flying everywhere.
The story, on the other hand, is mostly: so what? Persian king sends a different type of warrior against the Spartans, and the
This being a Frank Miller story, there are exactly two female characters - mother and wife of the King, respectively - and one of them agrees to sex in exchange for political help. And no, they don't meet, never mind have a conversation. I don't recall whether the mother-of-king character had a name, but then, this isn't a movie big on names. Apart from the two kings (Spartan and Persian), nobody's name made any impact on me, in any of the plot strands.
And then we get to the propaganda: this is painted as a small bunch of soldiers protecting the Land of the Free(TM) against a massive, overwhelming army ruled by a tyrant who claims to be a god. Given that the story opens telling us how children that don't fit the accepted norms are killed at birth, and given that the only role mentioned for women is to give birth to Spartan men, it's all pretty ugly. Yet we should think "patriots defending their land against the threat from the East, and it's okay for them to break the law to do so. We should admire them." I don't think so.