The majority of these reviews are coming from people who simply do not understand the storyline, and that's fine. The Green Knight is not supposed to be action-packed - it's cerebral, it's a story of virtue (or lack of it), moral questioning, humanity, and frankly, disappointment. Gawain's tale isn't a hero's journey.
Mesmerized by every frame, this movie did not feel like the run time was over two hours. It felt truly Arthurian and you felt sucked in to the pressure and over-assurance that Gawain felt in that moment. Little spikes of anxiety hit from time to time. Absolutely stunning and easy to follow tale, even if you are not familiar with the poem as my companion was not. Another reviewer wrote that he went home and thought of this until nearly 4am - as did I, unable to get out of my car once I returned home as I was reviewing certain topics that the movie brought up.
One note - if you are hard of hearing, you're going to want to absolutely use a captioning device. The audio was a struggle at times for me and I did miss chunks of dialogue, so I will be returning for another showing this week.