300's focus is clearly set on Epic. I have seen several scenes from 300 before and some of the "good bits" have been spoiled for me so keep that in mind.
300 is basically a movie about the famous fight at the cliffs of uhm... Thermopylae? The film pretty much begins when King Xerxes of Persia sends King Leonidas of Sparta a diplomat to negotiate a tribute from the Spartans to the empire of Persia. King Leonidas does a faux pas however and makes a large mess of the diplomatic negotiations. Due to his behavior Sparta faces war. The problem is however that according to Sparta law Leonidas have no right to start a law without the blessing of the oracle. He doesn't receive the blessing of the oracle but dismisses it and marches anyway. While he marshes and fights at the front against the Persian army, his wife fights against the bureaucrats at home.
Did you get all that? Pretty complicated setup for a movie that has the sole purpose of showing one single battle. The main problem with 300 though is that it has a knack of dragging out the fight scenes and the scenes that aren't fight scenes have the problem that you really don't care about the Spartans struggle. Leonidas and his 300 friends are really nothing else than brutes bent on fighting Persia because of a faux pas. The Persians are also pretty stupid because Xerxes only seem to march for the sake of pride, telling Leonidas that he doesn't care for anything Greece can offer - only the submission of their leaders.
300 is at the end of the day a pretty poor movie. Acceptable in it's own right and (thankfully) pretty short in comparison to other movies. If it had some better writing it might have been able to truly live up to the epic it tried to become.