I think I grew up with King Arthur. I knew all about Lancelot, Tristan, Gawain, Kay, and all the other knights of the Round Table before I was out of Middle School and I had a list of every one I had come across. I even managed to order them by their fighting skills.
Then I got to high school and I realized there was much more to him than that. There was an historical context in post-Roman Britain 410 to 600. That led to a great deal of reading about the source materials, their flaws, their dates of production, and a whole lot of insecurity about the topic. The fact is that there is so much we can never know about Arthur, his men, his battles, his location, the dates of his career. We won't ever know what he looked like, the details of his last years; such is a perfect opening for a fiction writer.
Which is why I don't get Arthurian movies at all. In King Arthur he and his men are Sarmations? But that tribe hadn't been active for centuries by 410. In his opening dialogue Arthur speaks about a contemporary named Pelagius; but Pelagius had been excommunicated and outlawed from all Roman regions before 400.
Then there are the more subjective flaws. Arthur allies with Picts (of the Highlands) while fighting against the Saxons who have landed on the southern coast. This in the fifth century, when all government had fallen apart and traveling the length of the island would have been a feat in and of itself. Rome was dead before Arthur was active, he could never have been its servant. Oh, and he might have had the money for metal body armor, but not one of his men would have, leather armor, wooden shields with leather or metal plating, and iron swords were the armaments of the day.
Tristan is made out to be a falconer. Warriors didn't do that, knights of the later Middle Ages did. Besides, Tristan was a figure of myth who was added to the Arthurian cycle later and all we know he did was slay a dragon.
Numbers are an issue, too. The economy of fifth century Europe had fallen apart, and farming was ragged. There was no means of supporting a large group of warriors, and farmers would not be asked to fight in a standing army until the modern era. That the Battle of Badon could have happened in any way as it is portrayed is laughable.
First Knight is no better with its shiny knights and high morality. A post-Roman king who didn't kill a man who looked at his wife would have lost the respect of his warriors. If Arthur hadn't conquered a kingdom with a weak ruler or no male heirs someone else would have. That covers my issues with Lancelot and Guinevere.
Tristan and Isolde? I can't help but smile. Originally the story involved a dragon, a knight who took credit for Tristan's (Drust's) kill, and the maiden who healed him and fell in love. That movie is an awkward combination of the romance as first seen through Thomas of Britain and a post-Roman Britain that could never have existed.
Can't we just have a movie involving Arthur where everything we know to be true is kept to and the poetry is in the plot, the characterization, or even the politics of the period? It would be so refreshing for a change.