Within my memory, there've been only a couple films featuring the legend of King Arthur. However, one of them released in 1981, EXCALIBUR, is the standard by which all others, past and future, must be judged. It's positively stunning in its excellence, and a must-see for any devotee of the tale.
In a sense, EXCALIBUR is more a story of Merlin than Arthur since Nicole Williamson's fabulous, unique portrayal of the former overshadows Nigel Terry's role as the latter. However, the film faithfully depicts the Arthurian legend from his conception and birth at Tintagel Castle, to his death at the hands of Mordred. In between are all the other elements of the story one would hope for and expect: Uther Pendragon, the Sword In the Stone, the Battle of Mount Badon, Camelot, the Knights of the Round Table, Sir Lancelot, Guinevere, Sir Percival, the Quest for the Holy Grail, the Lady of the Lake, and Lady Morgana (a.k.a. Morgan La Fey).
A note of caution for parents of young children. At times, the film is intensely violent, bloody and sexual. (Gee, it sounds like any normal day at the office.) You are warned. And it's not a movie for squeamish adults, either.
The costuming is superb. The brilliant cinematography and film editing, combined with a magnificent soundtrack that includes "Carmina Burana" and "Tristan's Funeral March" (correction: "SIEGFRIED'S Funeral March") at just the right scenes, make EXCALIBUR absolutely awe-inspiring. You'll want to watch it over and over. (I've talked myself into wanting to view it again right now!) The final scene is one you'll wish you could extract from your TV screen and frame, with sound.
Oh, my! What a cinematic achievement!