The Plot: Much like the original "300" was a fantasy version of the Battle of Thermopylae, this is a fantasy version of the Battle of Artimesium and the Battle of Salamis. The film also depicts the origin of the god-king Xerxes.
The original film suffered from something of a split personality--the fight scenes themselves were entertaining, but the stuff going on at home in Sparta was rather dull. "Rise of an Empire" was more even--although its best was never as good as the best of "300," its worst was never as bad as the worst of "300." It's never a boring film.
The film also provides more back-story for the original. In one of the more fun parts of the film, we see the Battle of Marathon and King Darius, Xerxes' father, as well as just what drives Xerxes to make war on Greece. Pursuant to that, I liked how the film humanized the Persians. The disrespectful Persian ambassador who Leonidas kicked down the well in the first movie also took pity on the young Artemisia, who was abandoned on the street near death after spending years as the pre-teen sex slave of some rather disgusting Greek sailors after her family was murdered. He trained her as a warrior and she rose high in Darius' esteem. But her grudge against Greece burned for years (given the horrors she'd experienced, that's not really a surprise) and this drives her actions throughout the plot.
(More on this later, as that was one of the film's weaknesses.)
Rather than being depicted as masked (so killing them isn't as upsetting) mooks, we also see Persian characters who have faces, names, and some bits of personality. Although those could have been developed a bit more, the fact they even put in the effort in the first place is a good thing.
And like the original, the battle scenes are fun to watch. Although some people have mocked the depiction of a horse and rider deployed in a sea battle, when that actually happens it's well-done and actually makes sense tactically.
Obviously this is a historical fantasy so expecting Eva Green's Artemisia to hew too closely to reality would be a bit much, but the movie takes her way too far. They depict her as being the architect of Xerxes becoming a godlike being (minor spoiler--he doesn't start out looking like a bejeweled escapee from a bondage club), killing everybody who might advise the empowered Xerxes against a war of revenge against Greece, and basically being the mastermind of the entire situation.
Artemisia has gotten a lot of praise even from reviewers who otherwise didn't like the film, but this was overkill. I've written another blog on how Artemisia could have been handled better--you can have a powerful female character without making her that overblown. In real history she had a great deal of influence over Xerxes, but the filmmakers took that way too far. Making Artemisia that powerful made Xerxes seem weak--although an interview with one of the people involved in the film said Xerxes at his core is weak and insecure, there's having a tragic flaw and then there's just being hapless.
Also, Artemisia is supposed to be this terrifying warrior and commander but for the first part of the film she's distinctly underwhelming as an admiral. Historically Artemisia was one of the most impressive commanders at Salamis, to the point Xerxes remarked that his male commanders (who lost) were women, but his women were men. She actually comes off as rather incompetent at first.
Another area where the characterization wasn't strong was Queen Gorgo, Leonidas' widow. In the first movie, while Leonidas held the line at Thermopylae she tried to rouse Sparta's government to send reinforcements, even submitting sexually to the slimy, ambitious, and rather cruel Theron. When Theron shamed her and she killed him, revealing he was in the pay of the Persians, the Spartan assembly immediately demanded war. Yet in this film, she's depicted as being so broken up over the death of Leonidas that she refuses to support Themistocles' all-Greek war effort. Regardless of whether she would be able to even stop Spartan involvement after that, I really, really doubt the fierce woman depicted in the first film would even want to. And then she calls out Themistocles for supposedly wanting to put a sword in her son's hand--never mind that in the first film the sons of Sparta's ruling class were taken from their parents and basically raised in barracks and this is why they're such awesome warriors.
Finally, in terms of cinematography the film is dark. Not in terms of content or atmosphere, but it's just dark and hard to see things. The soundtrack is also overpoweringly loud in a few places.
Great concept, but it didn't live up to its full potential. It's a good movie to see--at the dollar theater. 5.5 out of 10.