The Merlin Trilogy

Mary Stewart's Merlin Trilogy consists of The Crystal Cave, The Hollow Hills and The Last Enchantment (plus The Wicked Day, which is part of the same continuity but from a different viewpoint).

The series, as you might guess from the collective title, tells the Arthurian legend from Merlin's (and later Mordred's) point of view, from Merlin's early childhood to the Battle of Camlann. It takes a Demythtification approach (except for Merlin's visions and ability to light fires without a flint, which appear to be real).

Tropes used in The Merlin Trilogy include:

A Man Is Not a Virgin: Averted. Myrddin/Merlin is a virgin until he hands over his powers, and his virginity, to his successor. In fact, the one time he tries to have sex with a woman, he fails. He states that he had to choose between his powers and sexual prowess.
Ax Crazy: Most of the Orkney brothers to a degree, but especially Gaheris.
Bilingual Backfire: Merlin is captured by some bandits who are discussing in their language what to do with him, thinking he doesn't understand, until he tells them in their own language who he is and what will happen to them if they don't release him.
Broken Bird: Ulfin, who spent his childhood being abused in every possible way by an evil Druid. It left its mark.
Death by Childbirth: Arthur's first wife, Guenever (drawing on a version of the legend where Arthur had two or even three wives by the same name in his life).
Grave Robbing: Merlin scares the crap out of one unfortunate who tries this by sitting up and talking to him.
Infant Immortality: Very, very much averted.
King Arthur
Merlin and Nimue: Merlin and Niniane truly love each other and she innocently mistakes him for being dead when she buries him in the cave.
Old Retainer: Ulfin is rescued from effective slavery (and death when his master dies) as a boy by King Uther. He repays this with absolute loyalty and rises to be Uther's most trusted servant, going on to a similar position with King Arthur after Uther dies. He's also the only person who actually seems to mourn Uther's death.
Prophecy Twist: Merlin's prophesies often turn out this way, most notably the one about Merlin's own "end" (it was much less cruel than anticipated, and did not actually mean his death), and the one about Mordred being Arthur's doom (the inevitable tragedy isn't really Mordred's fault at all; it's largely the result of some terrible misunderstandings and unfortunate accidents).
Self-Made Orphan: Gaheris here is a raging psychopath who, in The Wicked Day, beheads Morgause after catching her in bed with a lover.
Shoot the Shaggy Dog: Arthur spends the entirety of The Wicked Day trying to create and maintain a peaceful, unified kingdom. Mordred spends it trying to escape the prophesy that says he will be Arthur's doom. In the end, through a series of unfortunate accidents and misunderstandings, they both fail catastrophically and end up killing each other.
Surprise Incest: Morgause, Arthur's half-sister, bewitches him into sleeping with her, and he only finds out afterward of their relation to one another. It's also implied later that Morgause's own son has these feelings for her.
Sweet on Polly Oliver: Nimue takes advantage of Merlin initially mistaking her for a long-dead boy called Ninian to dress as a boy and become his apprentice. Arthur eventually points out that she's a girl, causing some relief for Merlin.
Tear Jerker: Several times over.
Tongue Trauma: Casso sees more than is good for him in an evil king's castle and has his tongue cut out to stop him reporting it. This backfires when Merlin has him taught to write.