So I've seen 300 twice now, and I figure it deserves some comment.
300 was ... well, it has its goods and its bads. On the good side were the stylization (mostly) and the fact that the movie gets the heart of why Thermopylai is a story that has endured for 2500 years as one of the greatest feats of arms in the annals of mankind. On the bad side were certain pieces of dialogue and certain alterations to Spartan society.
Let me say before I turn to each of those items that 300 was not as good as Gates of Fire. Maybe that's unfair, because one is a graphic novel I haven't read that was turned into a movie, and the other is a regular novel that hasn't been turned into a movie, but to the extent that you can compare across genres there's just no comparison. One of the main reasons for that difference is that the characters in Gates of Fire are not (with one notable and important exception) trying to be heroes.
300, on the other hand, takes its inspiration from the extraordinary wave of patriotic fervor which swept all Greece in the wake of the Persian Wars. From the Greek perspective, Greek valor and the Greek way of life had triumphed over the monolithic empire from the East, an evil empire ruled with an iron fist by an eviler emperor who commanded alien hordes of slave soldiers and bought his enemy with his fabulous treasury, a man and an empire that stood against all that was good and right and happy in the world.
It's all nonsense, of course. Xerxes probably did have a fearsome temper, and he probably did lose perspective over the whole Greek affair, but Achaemenid Persia was in fact a great fountain of civilization (more "Greek" advances at the time of the Persian Wars had come out of Persian-occupied Greek cities than had come out of the Greek mainland) that was actually a very gentle and humane empire run on a quasi-federal system. Sparta was a police state whose entire society was built around preventing a massive slave revolt; Persia was the empire that sent the Jews back to their homeland with orders to rebuild their temple and worship their god in peace. The idea that Sparta defeated Persia in the name of freedom and civilization is transparently nonsense. But that was what the Greeks themselves honestly believed at the time.
This perspective informs every aspect of 300's stylization. The Greeks are nude (or as nude as we can get away with making them in mainstream American cinema) because the nude figure with shield, helmet, greaves, spear, and sword is the ancient Greek artistic convention for "hero." The Persian archers are dressed exactly as they are portrayed on vase paintings from the time, right down to the pattern on the fabric - as recalled by vase painters who were veterans of the war and vividly remembered every detail of their alien foe. Xerxes did not, of course, have gunpowder, war elephants (Persia didn't extend to India), or war rhinoceroses (nobody has ever had war rhinoceroses). But all that is meant to convey the perceived alien-ness of the empire. The Greeks do not generally fight in phalanx, but Leonidas explains the phalanx's fighting style in dialogue, so the moviemakers knew. It is just that they wished to display the heroism of the Greek fighters according to the conventions of American storytelling, where heroic fighters fight singly or in pairs. The one scene of actual phalanx fighting is a better on-screen depiction than anybody else has ever achieved (although still of rather poor quality absolutely, to be fair). They even have Gerard Butler play Leonidas with a Scottish accent (the tradition of translating the Spartan dialect as Scottish goes far back).
The movie's depiction of Sparta herself is hit and miss. I think it's clear that Frank Miller gets Sparta, but I am not entirely happy with the way he conveys that understanding. To really understand Thermopylai, you have to understand the Spartan way of life - Sparta as it was just before its society self-destructed in the aftermath of the Peloponnesian War. You have to understand how deeply these men loved their women, how deeply they partnered with them, and how earnestly - almost naively - they believed in the martial virtues. In 300 Leonidas' wife Gorgo stands for essentially all of Spartan society - that Spartan paradox of the warrior housewife, a woman who is thoroughly domestic and simple and humble in her way but whose virtues imbue her with a bearing most regal and make her quite as fearless as any hero. Now, it is important to understand that about Spartan women, to understand the sorts of families these men willingly left behind forever and to understand the sorts of families that made them who they were. You have to understand what they were fighting for to understand why anybody cares about their story.
Gorgo was, by all accounts, a most extraordinary woman. The trouble is that Miller invents a subplot wherein "the council" and the ephors are bought off by Persian gold, to give Gorgo a homefront war to fight. This shows her character to the best advantage, but it also depicts a fictionalized and un-lovable Sparta. To be sure, Persia fought with its gold as much as its soldiers; that's only rational foreign policy. But there is no evidence that they ever corrupted Sparta, and the ephors and the council are thoroughly fictionalized. The ephors were not a band of diseased and lecherous mystics; they were acclaimed as the oldest and wisest Spartan citizens, who served as senate to the kings' executive (our own Senate was heavily modeled upon the ephors' example). Indeed, we are told that the ephors told Leonidas he was taking too few men to Thermopylai (to which his famous reply: "Rather too many for the business at hand"). And Miller presents "the council" not as the body politic of Spartan citizens (and therefore the Spartan army) but as a bunch of professional politicians - and this dichotomy between the politicians and the warriors drives Gorgo's subplot, whereas in reality there was no such dichotomy. So it is easy to understand why Leonidas loves Gorgo so, and it is easy to understand what sort of woman she was, but as for Sparta itself the audience cares not a fig.
And that's a serious flaw, because the reason Thermopylai is important is because the Spartans decided to leave their beloved homeland and their families and die. The battle itself was indeed a spectacular feat of arms, but at the end of the day the allies held for only two days and their stand was of doubtful strategic importance. At best it stiffened the spine of the Greek allied congress to fight. If Greek civilization is what they were fighting for ... well, they were also fighting against Persian civilization, and that is a cause I find of doubtful nobility. But these were men who loved their families and loved their country, and when those were threatened they chose not to cling to them but to go far away from home and die. They could have sat at home and waited for the Persians to come, enjoying the time they had left - instead they chose to separate themselves from that which they loved in the hope that somehow it might be preserved. When the goat path was discovered they could have retreated, lived to fight another day - but they found they could not and still be true to what they were fighting for. They fought for Spartan laws, Spartan families, Spartan wives - and they could not run away and live Spartan men. They did not expect to come back, and they went anyway. They say that as her husband marched to the Gates Gorgo asked him what she could do to help. "Marry a good man," Leonidas said, "and bear good children." That - not the men they killed, not their warped view of the Persian Empire - is a story worth telling and retelling.
I didn't watch a lot of Babylon 5, but I remember an episode that struck me. A Minbari is trying to understand Christianity, and he asks a human monk what the emotional heart is of his religion. The monk thinks for a moment, and replies that it is not the Crucifixion, nor the Resurrection. It is the night Jesus spent in Gethsemane, when he was struggling with the full weight of realization of what was to come ... and decided not to run away.