I think they clearly stayed behind to block the Persians with the direct goal of keeping Greece Greek, and further, they did so with the clear knowledge that they themselves would almost certainly die. Truly heroic in every way.
My point was that better historical accuracy makes for better historical understanding (and in my opinion better movies), and Spartans were not freedom fighters as we think of the term. However, they were preeminent warriors and not willing to part with self-rule.
Such historical figures need not be just like us to teach us lessons and deserve our respect.
Very well said, SampleMan. Thank you. To the extent the film manages to teach such lessons (even in part) and induce such respect, it appears to be worth seeing (I simply can't stand most Hollywood offerings).