Eva Green & Lena Headley are two great actresses so I'm sure (no matter if this movie were bad) they would both perform great in their respected roles. I'm been a fan of Lena Headley as an actress (even before game of thrones) and Eva Green rivals her as a top notch actress so good casting on the female leads.
300 used the words Sparta, Thermopylae, Persia, Leonidas , Xerxes and the number 300.
Apart from those words/ names being used it had nothing whatsoever to do with the history of that event. Even the geography of the pass was wrong. the military strategy was wrong, the characters were wrong, the religions were wrong, the cultural information was wrong.
There was so much screamingly wrong it was difficult to watch until I switched off any idea that this was Spartans, or Greece, or Persians. I thought Conan the Barbarian and then it was fine.
As a fantasy film under different names 300 would have been fantastic.
As a historical drama it was a pathetic schoolboy mess.
Presumably this one will be similar. So just don't expect it to be anything to do with history, lie back and enjoy a completely unconnected fantasy.
You are correct, and me being Greek I can relate to what you're saying, but remember the movie was based on Frank Miller's comic book and not the actual history, and as all comic book fans know Miller is quite surreal and over-dramatic in his comic books.
So, if you were prepared for it (which if you are aware of Miller's work then you would be) it was fantastic to watch. But I agree the relation to the actual history is very small.