300 is a good, entertaining movie. Some might be unhappy with its glorification of warriors. But I see the Spartans' actions as purely defensive, and so not without redeeming value. Homophobes may become uncomfortable at all the bare-chested manly men, their spears repeatedly thrusting through sticky bodies. (Paging Dr. Freud...) But I hardly consider any of these fatal flaws. 300 is a solid film, despite the cast of unknowns. It's also a technical achievement of high order, due to being filmed entirely against green screen, and all the backgrounds being created later. Even if you don't like war movies, I don't think you'll be bored watching this movie. They did a good job mixing in a lot of different elements to keep it from becoming boring. Oh, and take your girlfriend - she'll appreciate all the beefcake.
That said, though, do not in any way confuse this well made and engaging piece of fantasy entertainment for actual history. It isn't. Enjoy it for what it is: A fun movie, but one that doesn't worry overly much about getting all the historical facts right, since they would get in the way of the entertainment.