It used the same formula as the 1st movie, a simple story with lots of action. I think where it falls short is it didn't have any really interesting characters besides Artemisia. With the exception of Themistocles the Athenians were just your standard variety warriors/farmers, there was nothing interesting about them, where as the 1st movie was about the Spartans a warrior culture, this made the movie far more interesting. I think if 300 Rise of a empire included the Spartans more in the story it would of been a better movie, saving them for the last 5 minutes of the movie was a missed opportunity.
It was still a decent summer movie but I doubt I'll watch it more then once... Well maybe twice so I can see Eva Green naked again