Complete Monster: Eleanon, leader of the Lealfast, is a Jerkass with Chronic Backstabbing Disorder that takes his whole species along with him. He treats women, especially his sister, like garbage, and forces his sister to act as sexual bait. As the speaker for the Lealfast, instead of working for what is best for them, he deliberately alienates any allies that extend a welcoming hand to the Lealfast so he can retain control over them. In order to meet an Eldritch Abomination and secure a deal with him, he lets thousands of his own people get massacred in battle, then blames it on Axis. He then makes a deal with said Eldritch Abomination which enslaves the Lealfast to it forever. When he finds a woman, Ravenna, under a curse to not be noticed, he claims he can lift the curse, then instead modifies it so she becomes invisible to everyone but himself, forcing her to become his spy.
Salome. She was a horrible and vile person as the Duchess of Sildon in Coroleas and no one liked her, but even she didn't deserve the endless gangrapes and torture from dozens of men and a boar, then watching her son Erza be castrated, gangraped repeatedly and murdered in front of her and then left to die after days of this once her Icarii blood was discovered.
Moral Event Horizon: Ravenna, when she betrays Maximillian and then has him killed. She's just lucky that Ishbel took mercy on her for being pregnant with his child and could resurrect him.
The fact that he's no longer an arrogant ass (due to his Character Development in previous books) might contribute to it as well - the fact is that he now recognises how flawed he is and how mistaken many of his actions were, and he's turned out better for it.
Squick: The usual coming from a Sara Douglass book.
Tearjerker: There's many in-universe examples, but the most prominent tearjerker from this series is that it was the last set of books Sara Douglass ever wrote before dying from ovarian cancer.
The Woobie: As it is a Sara Douglass trilogy, there's more than a few.
Ishbel is the most prominent one. As an eight year old girl, her entire family died from a plague and she was the only survivor and instead of helping, the people of the town boarded up the house and left her to die no matter how much she begged and screamed to the point she desperately tried to kill herself with her family's corpses. Thankfully she's taken in by the Serpent Coil and becomes their High Priestess so she does get to know happiness for a time, but then she's forced by the Great Serpent (Aka Light) to marry Maximillian and have his child. Thankfully he's a good and understanding man who gives her the choice to leave the marriage after a year if she wishes to, but because of circumstances beyond their control, important people in the Outlands die and Ishbel and Maximilian are suspected and flee, but Ishbel is kidnapped by the true murderer and his henchmen, heavily sedated with drugs which effect her and her unborn child badly. It only gets worse from there, she loses the baby moments after it's born as it's sacrificed to Kanubai, she loses Maximilian and their marriage and has it rubbed in her face by Ravenna. And that's just the first book.
In the second book, she gets better as she becomes much more powerful, confident and grows as a person while genuinely growing to like Maximillian as a person since they finally have a chance to really get to know each other over the events of the book, but as the same time she has to deal with Ravenna's jealousy, hatred and belief that Ishbel is going to kill Maximillian and betray everyone and everything to the One and Ravenna even tries to kill her because of it, not to mention Maximillian's death, thankfully she can save him but it was pretty horrific nonetheless.
Maximillian. At the age of 14, he was intentionally thrown into the Gloam Mines for seventeen years and suffered many horrors due to mining accidents and some of the guards torturing him for fun and by the time he'd come out of them, he was forever changed and still suffers from the memories from time to time. Through all of this, he meets Ishbel, loses her and then while they can rebuild their marriage and become friends for real, he has to be the Lord of Elcho Falling (Which seems to be near impossible since he can't access most of his power) and deal with Ravenna's jealousy and trying to control him and his life at the same time. It only gets worse from there due to the odds stacking against him but in the end everything turns out for the best.
StarDrifter. He witnessed the death of his granddaughter Zenith during The Wayfarer Redemption and it was all his fault, plus he survived the fall of Tencendor and the deaths of everyone he loved and cared for and lived embittered for five years with the guilt of Zenith's death without his wings. The worst part is that he lives in Coroleas, aka one of the most vile places to live in the world. Thankfully he finds out Axis lives and has a purpose again and from there, things get better for him.
Axis at first. He's dragged out of the Otherworld against his will and separated from his family by Isaiah and over the period of the trilogy has to deal with all of his flaws and mistakes as well as the fact that he's lost everything (Especially the Star Dance) and has to start all over and might not even end up back in the Otherworld when he dies for good. Thankfully StarDrifter is still alive and they are reunited and Axis learns how to reconnect to the Star Dance. He also finds out he's been brought back to be Maximillian's war leader and best friend which isn't too bad, but during this he ends up being manipulated by the Lealfast and betrayed by many people he cared for and nearly loses StarDrifter again.
What an Idiot: After the events of Threshold, the Threshold pyramid was abandoned and the Magi who worshiped it were all killed. Surely people would take note of this and not return, much less try to complete the project via the same methods as before, right? Wrong. Instead, new Magi with the exact same Functional Magic reemerge and not only complete the pyramid, but end up waking up two newabominations that try to destroy the world.