“300: Rise of an Empire” isn’t so much a sequel to “300,” as it is a companion piece. The film begins with a heavy introduction from Gorgo (Lena Headey), Queen of Sparta and wife of the late Leonidas. Gorgo narrated the Battle of Marathon, her monologue droning on ceaselessly and detailing the fight step-by-step. At Marathon, which pre-dates the first film, Themistocles (Sullivan Stapleton) shoots a fateful arrow that sets the film in motion.

After the prologue there are multiple threads. The rise of Xerxes (Rodrigo Santoro) — that humongous gold guy from the first film — plays out, as we see how he ascends from man to god-king. That’s tangential, as the meat of the film revolves around the naval battles between Themistocles and Artemisia (Eva Green), Xerxes’ right hand. These showdowns on the high seas are thrilling and take place concurrent to the events of the first film. There’s a real narrative pleasure to be had seeing how different pieces of the films intersect. “300” was the main attraction, but “Rise of an Empire” is both the setup and behind-the-scenes feature.

This is a cartoonishly violent film. Of course, this comes as no surprise to anyone familiar with the aesthetic of the first film. In “Rise of an Empire,” there are your requisite amounts of impalements in slow motion, and gallons of blood that look like they’re from a video game erupt from gaping wounds.

Back in 2006, when the first film was released, this carnage was a revelation. Director Zack Snyder (a producer for this film, which Noam Murro directed) was hailed for the beautiful, yet brutal, images that were captured in glorious slow motion. Indeed, many likened it to a video game. I can’t help but feel that, in these eight years between the first and second films, the gleam has worn off. Films and video games have grown leaps and bounds with how they employ technology. This film is a sight to behold, but in this place in time it just needs a little more.

Stapleton’s Themistocles is your generic Spartan male lead. Short hair, scruff, chiseled abs and yet, understanding. He’s not worth writing home about. Headey, who’s proved her mettle in “Game of Thrones,” is largely relegated to the sidelines. The real reason to watch this film, beyond that of the visuals, is Eva Green’s stunning Artemisia.

Green delivers one of the best villain performances in a Hollywood blockbuster lately. Ironically, while speaking with Marc Jacobs of “Interview” magazine in 2011, she mentions being typecast as the villain something she sought to avoid.

“I hope I’m not being reduced to the dark femme fatale, because it’s almost a cartoon, one-dimensional, temptress kind of character,” Green said. “I like characters who have strong façades and then have secrets.”

However, Green was surely drawn to this role due to the complex and layered characterization of her Greek-born, Persian-allied Artemisia. She is a fearsome warrior and a brilliant tactician, but a backstory stained with tragedy and death is what led to the creation of this foe. Green fuels this character with equal parts deadpan calculation and hot-blooded fury, accompanied with just the slightest bit of humor.

“300: Rise of an Empire” has just enough to warrant a viewing, especially for those familiar with the series. The narrative complements the first film, yet can stand on its own, and the naval battle set pieces are entertaining. Ultimately, Green’s turn as Artemisia elevates the film beyond what it should be.

Grade: B-