I saw Sin City and liked it, so it's not just a Frank Miller thing -- it was this movie specifically. (Granted, there are legitimate reasons to dislike the Frank Miller style; I'm just not going to cover them here.) Three main factors, in order of increasing importance, made 300 a more painful experience than I'd have liked:
1. Movie fighting.
The combat in this movie shifted back and forth between tactical brilliance and idiotic graphical pandering, with very little warning or middle ground. The scenes where the Spartans stayed in a tight phalanx, fought off wave after wave of attackers, hid from arrows behind their shields, etc., made the battle come alive. And then the wave of attackers would falter, the Spartans would leap up and charge, and the battlefield would become a chaotic mass of intermingled bodies, with the Good Guys pirouetting between enemies, somersaulting baddies over their shields, performing choreographed spin thrusts, and simultaneously triple-skewering my suspension of disbelief.
This would have been more forgivable if they hadn't tried so hard to make the, well, real fighting stand out. "Look! The Spartans were really badass and this is how they really fought! Then they gained three levels and two bonus feats and ROLLED THE CRITICAL HITS!" just doesn't work.
2. Teh gay.
No, there's no explicit homosexuality in this movie (the one reference being where Leonidas tells the Persians that those pedophile Athenians have already stood up to him, so Leo's not gonna back down either). But ... holy crap, Xerxes is lord high ruler of the drag queens. His makeup budget must be about as huge as his military one. You'll also notice, if you stick around through the credits, that the Big Erotic Persian Scene contains three transvestites.
Not enough? Notice that while Leonidas' manly manly men are unstoppable on the battlefield, all of Xerxes' onscreen victories are through bribery, temptation, and seduction. Pretty much everyone except the ultramasculine hero and his ultrapure wife gives in to the jewelry-heavy, silky-voiced man's wiles. Also don't overlook the repeated references to the Persian army being enslaved by their leaders -- how many times have you heard the religious right refer to the "gay agenda" and its attempts to "brainwash" or "enslave" our children? Look out, the Persians are going to contaminate our precious bodily fluids! Which leads me to:
3. Painfully Republican.
300 is not a subtle movie.
The very first thing Kady and I agreed on as we left the theater was that it was painfully heavy-handed. And the lessons it tries to draw are at once simplistic, convenient, and very dangerous.
Leonidas' 300 -- and more broadly, his city-state of Sparta -- are repeatedly shown as the sole beacon of freedom, justice, and the Greek way in a world of invading Persian faggots (see #2) and their liberal Athenian surrender-monkey allies. The Persians are an existential threat to all of Greece, but weak-willed politicians and a decadent populace are too blind to see it (especially after being infiltrated by a fifth column of false prophets and bought-and-sold governmental traitors). The Greek politicians initially united against Xerxes (remember the reference to those boy-loving Athenians telling him to sod off?) but have now sold out and would rather throw meaningless festivals and be bribed by bad guys than defend the homeland.
Any of this sound familiar?
It should. It really should. This movie is the argument, in a nutshell, that Bush loyalists have been jumping up and down and screaming at the top of their lungs since 9/11, and are still sticking to in the face of the Iraq war's disintegration. It's Ann Coulter and Michael Savage's shrill denunciations of all liberals as traitors and fifth columnists. It's right-wing blogs' insistence that Islamic terrorism is a threat to the very foundations of civilization and neocons are the only ones with enough clarity to do what must be done. It's culture warriors' denunciations of Teh Gay (see #2) and promotion of an idealized hypermasculinity and strict warrior culture.
Like those blowhards, the movie also suffers from a promotion of rhetoric over reality. On numerous occasions, Leonidas and/or other Sparta mouthpieces repeatedly promote how they stand for freedom, etc. However, look at what the movie (and the history) shows and it's a different story. Sparta is (correctly) shown as a harsh, totalitarian culture, where insufficiently strong children were killed and military strength was emphasized. And contrary to the movie's mythologizing about freedom, ancient Sparta was actually a slave society (those who weren't descended from Spartan blood were called "helots" and were officially serfs belonging to the state).*
In the movie, the only actual instance of Sparta defending freedom of any sort was their stand against the invading Persians. And even there, in reality, the Spartans were hardly alone -- they were certainly the heroes of Thermopylae, but not as the clear-eyed sole defenders of liberty the movie (and graphic novel) paints. The entire scene with the stupid council ignoring the Persian threat was, shall we say, entirely made up. So the movie got progressively more painful every time the rhetoric blasted in.
Look, I'm not the sort of guy who injects politics or ivory-tower lit-crit into everything. (For instance, I'm on record as saying that reading racism into Tolkien is absurd.) But "300" is such a huge, blunt talking-points instrument that it's in a category of its own.
This movie was a barrage of violence between ultramanly good-guy soldiers and demonized Middle Easterners intermixed with heavy-handed right-wing talking points. I've gotten enough of that from the news in the last several years. No, thank you -- won't be seeing this one again.
* To Sparta's credit, they had attitudes toward women that were incredibly enlightened for the time. Wikipedia's notes on Spartan women and adultery are an interesting counterpoint to the movie's treatment of the queen.