To put it about as bluntly as a slow-motion spear to the gut, “300: Rise of an Empire” just isn’t very good. If this film was a newborn baby in Sparta, they’d cast it out for the iniquities it possesses compared to its predecessor.

The original “300,” which was a huge commercial success back in 2007, was based on the popular 1998 graphic novel of the same name by Frank Miller (“Sin City”).

“Rise of an Empire” is inspired by source material that hasn’t even been published yet. Miller is currently working on “Xerxes,” a sequel to the “300” graphic novel, which is said to tell the story of the god-king’s origin and rise to power. 

That publication still has no release date in sight, which means that screenwriters Zack Snyder and Kurt Johnstad (both veterans of the first “300” film) were forced to take huge creative liberties with the story for “Rise of an Empire.” 

I can’t say if that’s necessarily a bad thing, because there’s nothing to judge it on except the merits of the first movie. Sure, “Rise of an Empire” captures that sexy, hyper-stylized design that “300” spawned in countless film and television rip-offs since its release. 

If judged on its own, “Rise of an Empire” expands the franchise’s story with a timeline that takes place before, during and after the events of “300.” 

That makes it both a prequel and a sequel.

We learn more about Xerxes (Rodrigo Santoro) as a character, which is cool. I loved seeing this edgy take on his humble beginnings and learning how he became the sovereign king of all Persia.

However, Eva Green (Casino Royale) is by far the film’s crown jewel. Her performance as Artemisia, commander of the Persian navy, is bold, tough, sexy and terrifying, all at the same time. She’s definitely the most fun in the bunch.

The writers lend some complexity to her character as well. Artemisia was a child slave who eventually proved her worth to Xerxes and eventually became the most feared naval commander in the Persian Empire. 

One of the biggest missing pieces here is a charismatic leading man. 

Gerard Butler’s over-the-top performance was really what made “300” so enjoyable. Sullivan Stapleton (“Gangster Squad”) steps in as Themistocles, a Greek general who leads his naval fleet against that of the Persians and Artemisia.

“Rise of an Empire” could have been a major star vehicle for Stapleton, just like it was for Butler a few years ago. But for now, the guy just lacks the screen presence for us to buy into his role. 

Where Butler frequently roared the fun but ridiculous vernacular of gym bros everywhere, Stapleton just grits his teeth like he’s constipated.

The first “300” also had a variety of locations and enemies for the Spartans to confront. All the action in “Rise of an Empire” takes place purely on the high seas. 

It’s like a graphic “Spartans of the Caribbean” video game that gets old quickly.

Grade: D