I read the graphic novel just before seeing the movie. With the exception of some of the 'monsters', the rhinoceros and the subplot of betrayal back at home, the movie hews pretty tightly to the book. One thing they keep faithful is that the religious authorities sold out for the invader's gold. I read this as a kind of indictment of organized religion, what with Leonidas' dialogue on logic versus superstition and all. I liked the sheer spectacle and the art of it all: it was operatic. Any messages within from the "sponsors" had better not be looked at too closely or the propaganda could backfire.
Another thing about Sparta that this movie conveniently glosses over is that they were slave-holders. Those pretty wheat fields were tended by slaves while the warriors in speedos and red capes sat around either training for battle or taking it easy (course, I doubt that was their dress of the time but anyhow..). Lycurgus, a predecessor to Leonidas and ideological father to Sparta is mentioned exactly once in book and movie. I'd suggest that the pushers of propaganda and jingoism could have chosen a better vehicle for their message: Lycurgus was darn near a communist according to some. He pushed for material equality amongst all Spartan citizens (note that the slaves were most definintely NOT citizens) and eschewed baubles, luxuries and the sort of non-essential garnishment of home, clothing and everything else that we see today. The only avenue for social one-up-manship was in the arena of martial skills. The only profession for a Spartan was 'soldier' and 'farmer' with the slaves doing the farmng and the Spartan collecting the production.
Lycurgus has at times, been lionized by some Marxist writers in the past for his disdain of luxury and dictation of material equality of citizenry. The Spartans were not allowed to grow rich: any excess was taxed away and all citizens remained equal in land, house and possessions. I don't think the Competitive Enterprise Institute would like that.
The Persians by contrast, enjoyed luxury, often times sumptuous. They also enjoyed the "easy life" if they were in a position to get it. Obviously being in a position to attain the "easy life" means one must control a lot of slaves or extract a lot of tribute from their subjects. This suggests that we 'Merkins'

are more like Persia then Sparta. It's a case of "don't look too closely" and "dont think too much", just sing along.
If we insist likening ourselves to the Spartans, it is we who today, sit in idleness with time only for football while low-paid Helots from China make our trinkets and those from south of the border flip our burgers and mow our lawns and do some of our fighting for us while we sit around admiring the BMW in the driveway and chortling about how much money we pulled out of our last refi. The difference is that none of our pasty arses could even come close to the skill and discipline of a Spartan. Most us are more like that of the Persian Satrap who reclines on a cushion in a palace all day while others do the growing and fighting and dying.