I went to see 300 on opening night. It is a testosterone fest to be sure. Lots of action; however, if you are looking for historical accuracy look elsewhere. I did not read the graphic novel by Frank Miller of the same title and I am sure it is just as exciting and visually thrilling as the movie, but a lot of liberties are taken with the story. To be sure, I do not think the greek phalanx functioned in the way depicted in the movie - that being line up defensively until you engage the enemy and then spin and trash in circles. The Spartans wore a good deal of bronze armor and were not the naked guys with cloaks depicted in the movie. Also, the combined force was somewhere in around 3 to 4 thousand (300 were spartans). It was visually stimulating but probably not the way it happened.
That is really my only real complaint. If there was no real battle at Thermoplae in 480 B.C.E., I would have no complaints at all. It was a fun movie, lots of interesting soldiers, a goat smoking a pipe, body piercing Xerxes who was a bit of giant, archers that did in fact blot out the sun (a nice visual). It is a great underdog story, they are all killed to a man but it was the price of duty and honor. I still say see it, just forgive the historical short comings.
At the theatre I went to some folks were upset that Leonidas did not kill Xerxes in the end. I think that would have stretched history a bit too far.