I've read several modern retellings of the Arthur legend--enough that I have trouble getting through the more traditional high chivalry versions, because "my" King Arthur was a Celtic or Romano-Celtic warlord trying to hold back the Saxons, and I'm just not as interested in the other kind. I lost interest in The Once and Future King, and I'm trying to force myself to read Le Mort D'Arthur to figure out what aspects of the Matter of Britain would've stood out for the characters in my 1805 WIP, but I'm finding it a slog. Probably a failing on my part, but once I get a vision in my head of what a story is, I cling to it stubbornly.
Bernard Cornwell's trilogy is probably my favorite Celtic Arthur, and Excalibur (1999) is a fitting end to the trilogy. It has plenty of gore and horror, and honor, courage, and loyalty to balance them out, and all with a sense of a growing shadow throughout, because you know how it has to end.