Not bad. Some quick notes: (SPOILERS)

Pros:
- Good story, good action
- The explanation of the sword in the stone (wedged on Arthur's father's tomb)
- Bors' and the knights' antics
- No weird magic, Merlin is just a rebel chief
- Many images: Arthur with the banner on the hill, the horses at the end...

Cons:
- The main one: if this story supposedly inspired the legends, why does it have nothing to do with the legends, apart from the main character and a very vague infatuation of Lancelot for Guinevere? How can this Galahad have inspired the "pure" Galahad of tradition, and so on? The knights could have had different names.
- Stereotyped view of imperialistic Rome, bad Christians, violent Saxons. Especially the violent Saxons! This is prejudice! :D The Saxon chief was very cool, though.
- Strategically, it's bad to let your hawk go before a battle, and also to ride in on a white horse and then *dismount* in the middle of the enemies.
- A narrator that talks on his funeral pyre?...
- Clothes and armours. Some things were fine, but others, such as Arthur and Lancelot (and even the Saxon chief) wearing leather tights and a doublet, were not; in the night scene on the ramparts I thought I was watching Branagh's Hamlet.
- What about Pelagius? The viewer might wonder why he is persecuted for vaguely saying that everybody can choose his own destiny.
- What about the archaeological discoveries mentioned on the screen at the beginning? It makes one curious and not even the official web site says anything about it.

Nitpicks:
- A frozen lake in Scotland? It's cold, yes, but...
- No crossbows back then, I think
- Clive Owen is the most depressed actor on earth. He barely cracks a smile at his wedding.

There's more, both good or bad, I may expand on it.