I liked 300 - but as the adaptation of a comic, rather than a historical movie. After all, the Spartan hoplites would have been wearing full armour in reality. The director, I think it was, said he wanted to get the look of the Ancient Greek vases, where they were portrayed wearing little more than a cloak and a helmet.
I think it actually got the basic story across very well.
And Gerard Butler's accent didn't bother me - after all, none of the actors were Greek, and the Greeks do (and did) have regional accents. It was rather like an adaptation of the Gospels that was done a few years ago, where all the disciples had Scottish accents, and the people from Jerusalem had posh English accents - because it does say that the Galileans had a regional accent, and obviously no-one was speaking Aramaic in the production.