Artistic treatments of the Arthurian legends date back to illuminated codices from the Middle Ages. Thereafter the first, and one of the greatest, attempts to bring the stories into a novelistic form was written in the late 1400's by a knight, Sir Thomas Malory, entitled La Morte d'Arthur ("The Death of Arthur") which is probably the most famous work of English letters proceeding Chaucer but before Shakespeare. Even later renditions include T.H. White's "The Once and Future King". By the 20th century, theatrical adaptations began appearing as well, including "Knights of the Round Table" (1953), Disney's "The Sword in the Stone" (1963), and the musical "Camelot" by Lerner and Lowe which was possibly the most popular rendition of the story before "Excalibur". These last renditions, although they have their appeal, cannot measure up to the movie "Excalibur" which was largely based upon Malory's original tome.
Many here have detailed very well the merits of the film, and since most people know the story, I will keep this short. The reason why this is the best of the Arthurian-based films is its imagery and its dedication to the original Arthurian myths. The entire look of the film, which I have not seen in a movie since, reeks of Medieval Legend. The lush forests, the huge castles, and the glittering swords give a visual and dream-like reality. This is NOT how it was in the Middle Ages. This is how people in the Middle Ages would have liked it to have been, which is the entire point of the Arthurian myths. The filmmakers of Excalibur understood that myth is about dreams.
Several moments in the film are inspired directly from Malory and earlier Medieval codices. For example, several Medieval illuminated manuscripts feature the hand of the Lady of the Lake bestowing the sword Excalibur to Arthur. Strangely this episode, which becomes an important theme throughout Excalibur, is lacking from other theatrical versions and yet it is central to the original myth. Another is the strange rhetoric that Arthur and the land are one, and when Arthur becomes ill, the land of his kingdom becomes barren. This concept was a widely held belief in the Middle Ages: that the sovereign was essentially married to the kingdom.
Another aspect that makes this film outstanding is the portrayal of Merlin by Nicol Williamson. This was possibly the best Merlin ever to come to the large screen. Some of the most humorous moments of the film occur with Merlin. Instead of being the absent-minded wizard of "The Sword in the Stone", he is the last of the Druids, a race giving way to Medieval Christians. Worth the price of admission. It is sad that he obtained very little recognition for this portrayal.
The fact is, a viewer either experiences "aesthetic arrest" with Excalibur, or he or she doesn't. If the scenes when the knights go riding through countryside with their pennants flying behind them doesn't give you the shivers, this is not and will never be your kind of movie. If Malory had lived to see this film, he would have been awed and proud. Malory gave Arthur to the world, and Excalibur gave Arthur back to Malory.