If you're going to play the King Arthur game, you might as well have some fun with it. Director John Boorman certainly did with his 1981 "Excalibur," which was a reprise of one of the old Camelot tales, featuring Arthur and Merlin and Morgan le Fay, as well as the Knights of the Round Table, the Lady of the Lake and so on. The movie had wizards and action and a strong cast (including up-and-comer Liam Neeson in the role of Sir Gawain). With the usual caveat about outdated film technology, the picture can still be recommended as a fun watch.

"The Green Knight," a new Arthurian romance by writer-director David Lowery ("Pete's Dragon," "A Ghost Story"), is not much fun. The movie is low-key and in parts obscure, and its relative lack of action will be a drag on some viewers' patience. It could use a good dragon.

The story is drawn from the 14th-century Arthurian tale "Sir Gawain and the Green Knight," a work that has exasperated untold numbers of college students over the years. Gawain is now played by Dev Patel, an actor who doesn't yet project a full-blooded star presence but is solid in the role. However, his performance is eclipsed by that of Alicia Vikander, who plays two characters — a high-spirited bordello girl named Esel and a mysterious noblewoman called the Lady — with such unwavering focus that one could be forgiven for not noticing that the same actor is playing both parts.

It's a quest story, of course, set in a world in which Christianity (symbolized by the metal halos worn as crowns by the royalty) still rubs up intimately against the old pagan culture (there's a talking fox). The season is Christmas, and as King Arthur (Sean Harris) and his knights ready themselves for the annual revel, an unsettling figure enters the royal hall. It's the Green Knight (Ralph Ineson), a character with barklike skin and an imposing body that looks as if it were carved from a tree. (He might be an Ent escaped from one of the Middle-earth books by J.R.R. Tolkien — a renowned translator of "Sir Gawain.")

The Green Knight has a proposition to put to the king. It's a little strange. He offers a big, deluxe battle axe for Arthur or one of his champions to use in an attempt to behead him. If the assailant fails, he must face an identical assault by the Green Knight one year hence. Gawain, who is Arthur's nephew as well as a Knight of the Round Table, volunteers to take this problem off his uncle's hands, and he appears to win the deadly contest that follows with a single swipe of the mighty blade. But the Green Knight doesn't fall — he simply stoops to collect his severed head, reminds Gawain that they will meet again (like he might forget) and rides off on his horse.

One year later, Gawain sets out for his rendezvous with the Green Knight. It will almost certainly be fatal, but it is a matter of honor, and Gawain values honor above all other things. His journey is long and offers some eerie sights. Skeletons in iron cages hang from trees along the road. An ancient crone sits at a small table with a white blindfold over her eyes. Towering spectral figures drift by in silence. Gawain encounters a young woman named Winifred, who is quite odd. "Are you real or are you just a spirit?" he asks her. "What is the difference?" she replies, openly inviting a pop on the head.

As he draws ever closer to the Green Knight's home turf, Gawain is taken in by a noble lord (Joel Edgerton) and his spooky wife (Vikander). In their castle, whatever powers now run this world attempt to compel Gawain to compromise his virtue, to abandon honor. This is an interesting part of the story. Unfortunately, by the time it rolls around, some viewers, possibly bored to death, may have already abandoned the movie itself.