Noggins aren’t just severed in 300. They do full gainers that linger on moment-of-death grimaces and how director Zack Snyder’s idea of a chopped neck resembles chili with onions.

Frank Miller likes his interpretation of “graphic novel” literal, and this grisly epic is adapted from his take on the 480 B.C. battle at Thermopylae, a pass into the Grecian military state of Sparta.

Largely filmed against computer-generated backgrounds, the movie unfolds over that three-day stand of 300 Spartan soldiers, led by King Leonidas (Gerard Butler). All were killed by a Persian army of hundreds of thousands, but only after disproportionately depleting enemy ranks.

To paraphrase one Spartan, Snyder’s stylized filmmaking makes for many “beautiful deaths.” Many stunning single-shot compositions spring forth from a digital palette of gory gloom — stormy glimpses of Leonidas on a mountain, trees of twisted bodies, forts built of rotting corpses.

Leonidas trained his warrior fraternity to fight as a rigid, singular body, but the movie could use a little bit more of its source creator’s trademark anarchy. Miller is an executive producer, but 300 sorely lacks the co-directing imprint he put on a similarly filmed version of his Sin City.

Watching brownish blood splatter in near-platelet form is initially invigorating, but the violent ballet pulls the same pirouette time and again, lacking the unpredictable aggression of Snyder’s film debut, 2004’s Dawn of the Dead. 300 never invokes its butt-kicking right to gradually top itself for potent, visceral craziness.

The movie’s also no “groundbreaking” visual extravaganza. All those wheat-filled fields are missing is the brush of Russell Crowe’s hand from Gladiator. And, aside from more exposure of female nipples, night scenes are just like Nine Inch Nails’ video for “The Perfect Drug.”

Sadly, 300 feels like a disappointment Snyder would’ve made in his initial jump from the music-video world. But the only thing more deadly than constant sameness is constant seriousness.

Here, Sparta is a place where male babies are killed if they won’t one day be physically perfect fighters. Coronation goes to Leonidas only after many contusions, and showing a soft side to his queen, Gorgo (Lena Headey), and his child is frowned upon. 300’s wise twist on a teary goodbye is that there’s not one; Gorgo is as ruthlessly dedicated to Sparta’s survival as her man. She arguably quenches the film’s biggest bloodlust during a political power play in Sparta.

Plus, Leonidas’ soldiers have more abdominal definition than He-Man. No reluctant goat-herders or potters here, just killing machines willing to meet death. They don’t need faux-Braveheart inspiration, stifling narration or Butler’s freakish teeth gnashing on war-hawk soliloquies. Spartan nationalism correctly borders on psychosis, but the script rarely cuts loose with gallows humor, like Leonidas’ mouthy quip to Persian king Xerxes that he can’t kneel because of cramping.

Played by Rodrigo Santoro (Lost), Xerxes is an explosion of bling. Like Jaye Davidson in Stargate, Santoro’s appearance is androgynous, but his voice and height are digitally altered in a failed attempt at making him menacing. More frightening is Xerxes’ menagerie of monsters, like a chained troll unbound or an executioner ogre with blades for arms.

300 is well within its right to go over-the-top with their use. To hell with historical accuracy, as it’s not needed, or wanted, in this treatment of the tale.

But something’s wrong when an executioner ogre with blades for arms isn’t allowed to lop off heads in battle. Strangely, 300 pulls back on its potential for anything-goes craziness and mania. For a film with such artful decapitations, it has an awfully self-important head on its shoulders.