Unfortunately, it's 2 stars for me..
Recently finished the book series and compared to that this TV adaptation seems a very watered down version which is a shame. They have changed too much of the storyline already. Why not stay true to the books 100%? It would make for a better show.
The Winter King TV adaptation is a little too fantasy for me. Personally, I'd have preferred a darker and grittier adaptation. There are plenty of fantasy shows retelling the Arthur legend already, why make another? I have found Cornwells telling was absolutely fantastic because it was more historical and real.
The books do a good job of portraying what Britain was like at that time, showing the complex relationships between people's and kingdoms, the politics, religious tension, and the brutality of warfare in 5th century Britain.
Cast is hit and miss for me. Very diverse. Some of them do a decent job but most of the characters lack any depth. Not convinced by Derfel which is a shame as he's the main character. Arthur's just a bit boring. Merlin is literally the opposite of Book Merlin. TV Merlin completely lacks the complexity and personality of Book Merlin. Gundleus is your stereotypical bad guy clad in leather.
What irks me also is this is supposed to be happening in Dumnonia in Southwest England. I didn't realise they had such a mountainous landscape down there. They make it look like Scotland or North Wales. Too much fantasy not enough historical accuracy for the time and place.