Not only that, but "300" is a remake (with some liberal interpretation) of a much earlier movie called "The 300 Spartans" - it came out in late 1950's or early 1960's - not sure which.
The story is worth retelling only because it reflects a famous real battle in history and demonstrates a point that is worthy of study in all military colleges of any quality. If you find a place that gives you geographic advantages, you can do a lot more damage to your enemy who has to not only fight you but the terrain too.
The battle at Thermopylae ranks up there with the battles of Agincourt (see Shakespeare's Henry V and Bastogne (see any of dozens of movies about WWII.) I'm sure other history buffs could supply more names but I've made the point already.