Like others have commented, it is a show that doesn't know what it wants to be. If they had gone with "in a time before Arthur", as the opening credits suggest, then perhaps there would have been something worth watching. It could have easily gone on and at the end of the series, simply ended or have Arthur pull the sword from the stone.
Instead, the writers attempt (and poorly may I add) to intermix an untold story with bits and pieces of the Arthurian legend thrown in. This makes a mess of a story that just isn't remotely satisfying (Think Merlin without the chemistry between actors or a solid script). At one moment you are watching an action movie, the next you are expecting Edward and Bella to start pinning for one another (yeah, it's that bad).
The 10 episodes spend a lot of time drifting and not making good use of building the story or back story. I found myself doing other things during the show while waiting on it to get back on topic, not a good thing. A few typically strong actors fail terribly in this storytelling. Chief among them is Gustaf Skarsgard. someone whom I hold in high regard as an actor, suffers from interpreting the character Merlin in way that is just unrelatable. You don't cheer for his success or death, you just sit by and wait for his scenes to end so they can move on. Even after a few big reveals (no spoilers here), you just don't care and never relate to the direction of the character.
Two other relatively unknown characters to America audiences, Daniel Sharman (the Weeping Monk) and Sebastian Armesto (Uther) bring nothing to the story. Sebastian doesn't seem to know where is character is going or why he is there. Daniel must have mistaken the part as a dark side of an Arrow episode. It makes sense that we call him the Weeping Monk as you desperately want to weep in every scene he is in. I don't know his other work but this part and his approach to it fail miserably.
That said, Peter Mullan is scene stealing as a power-crazed, right-wing Father Carden. His evil, combined with his holy crusade, reminds Americans of some parties of our current government. He is a fine actor that takes a dull script and breathes life into it. Similarly, Devon Terrell, when interacting in a supporting role scenes, does an excellent job. Sadly, his character of Arthur is premature for this story but had he played by any other name, he would have brought another dimension to the show.
After struggling through all 10 episodes, I would be surprised that this gets a second season. With so many far better tales of old on various streaming services, there is nothing to make this one stand out.
Finally, Editing was hideous! You are watching this serious (at the best of times) drama and then there is this Monty Python cartoon transition between scenes. I literally wanted to scream every time they did it. It killed the mood and snapped you out of the moment. How the production team didn't see this and say no is beyond comprehension. If a giant foot would have come out of the heavens and stomped everyone between scenes, it would have been more appropriate. Scooby Doo had better scene transition than this editing monstrosity. I sincerely hope the story runners learn a valuable lesson and never, ever do that again (think lens flares by JJ Abrams)
As a silly aside, costuming was not well done. Not being picky but most of the clothes worn were machine stitched, had lycra, and other similar materials. I'm good with overlooking a few things but this really stood out and while not off-putting, it was rather humorous to see such a grand scale production cheapen by a lack of detail.
