Sir Gawain and the Green Knight is an absolutely gorgeous story that has withstood the test of time and come out far ahead.
It is a tale around how no one, no matter how devoted or dedicated or ideal, can live up to impossible standards - and how that's perfectly fine, because failure isn't the end. Confess, repent, pick yourself up and keep aiming for perfection.
It's a brilliant character study of a very good, and very human, man.
It's a epic and humorous Arthurian romance.
It's a PSA about creeping on hypothermic knights.
This story is the opposite of all of those things. It would be merely boring and crude if it was set in some 14th century monarch's court. Set during the reign of someone who's supposedly King Arthur, this film is downright offensive.
This movie amounts to a purposeless, plotless, unsympathetic waste of two good hours you could have spent playing with dogs or making a tent or calling your mother or SOMETHING, ANYTHING, other than watching a worthless coward stumble around what appears to a woodsier version of 1600s London. Skip it, read the original poem (there are a lot of great translations!), then watch the 1991 film if you want a great and very artsy adaptation.