The Warlord Chronicles trilogy by Bernard Cornwell is a wonderful twist on Arthurian myth, set in a more believable 5th century Britain. It's told from the perspective of Derfel Cadarn, a soldier who rose from the rank of spearman to become one of Arthur's trusted warlords, and then converted to Christianity and became a monk in his old age. I will say, though, that if you're looking for a traditional high-fantasy Arthurian tale, you should probably look elsewhere: Cornwell's Britain is a crumbling husk of Roman civilization, facing collapse under the weight of invading Saxons and internal strife. Magic takes a background role, and it's more ritualism than anything; a few druids, including Merlin, still exist, but it's unclear whether or not they actually have, or have ever had magic at their disposal.