Takes Liberties with the book, which takes liberties with Tennyson, who took liberties with... As the stories of Arthurian legend (maybe myth?) have evolved through re-tellings and expansions over the centuries, this retelling also goes in directions from Marion Zimmer Bradley's book, which openly created a different presentation and interpretation of the stories of Camelot. Morgan Le Fay, demonised in the Tennyson presentation where she had been a somewhat neutral character in previous renditions. Viviane had been the villain of most renditions meanwhile. I cannot profess to have read every telling over the years of the Arthurian tales, but being a student of multiple religious faiths including "English paganism" (not simply that of the Druids, but also the little people) I can see much of the potential of the book.
Unfortunately, the faith issue was not the topic of the movie, nor was the ability of Arthur, first through force against the Saxons, and then through conversion to Christianity of those same Saxons, to unite England. Instead we have the Saxons still attacking at the end in the movie. Instead, we have characters as sculpted in the book presented in a low budget production with leaps in the story meant for people that haven't read the book to get a sense of the voices. Acting does accomplish some leaps over problems in the story, but read the book, read the early texts, maybe then read the Tennyson rendition.
Could a big screen rendition handle this better? I doubt it would have enough time for the stories along the way, which contrary to the view of the director explain much of the book. A mini-series, as this originally was, with another two hours (this is already 183 minutes) could have better developed key aspects, such as Lancelot's marriage, and the important plotting Morgaine undertakes in Wales, as well as Gwenhwyfar's abduction and Igraine's death. Even the death of Viviane and Raven's prophecies were mishandled, losing key understandings of the different faiths. Maybe somebody with the time, budget, and in need of a sweeps blockbuster will try again, but then again, maybe the tale works only when transferred from the words on the page to the images of the mind.
Maybe the best that can be done with cinema is either the musical Camelot, or Monty Python and the Holy Grail - the Arthurian tales are too broad to cover in one presentation. That said, the migratory sparrows are dropping more coconuts around here, I need to go pick them up.