I have never studied about Arthur before, so historically and factually I am not the best person to comment on the depiction of King Arthur in the movie.
Its tale of honor, comraderie, leadership, friendship, treachery, bravery, slavery and above all freedom.
King Arthur - man of his words, leader who believes in doing what he preaches, puts the knights welfare before his own interest, compassionate, brave, skilled, one who stands up for the needy, whatever you need from a leader. He does not command his knights, his knights take up the battle for him. Lancleot asks- 'Is this Rome's quest or is it Arthur's'. In the final battle against the Saxons, the reason the Knights decide to fight, is for Arthur. Arthur proclaims, 'I do not fight for Rome, I fight for a cause which no man can probably understand.'
Guinevere - When she was rescued from bondage, I hardly knew that she is going to be such a fire-brand. She is brave, courageous and helps Arthur think for the Britons. She being rescued by Arthur himslef, is definitely destiny's design :)
"Finally I found a man worth killing"