This one...
and the prequel... (still in the process of "playing")
...touched me so much.
My favorite thing about this series is, that there is no "main boss", no "main villain", no single source of evil here; instead, we see how many people, who have seemed nice at the beginning, start to do cruel things for a variety of reasons. And all of these reasons are investigated and explained. I like when characters are well-written and get thoroughly psychologically analyzed by the author. Especially mad and dreadful ones, who seems to be something at the scale from just "jerks" to "unexplainable absolute evil" outside, but actually have a deep personality inside, and if we can peek into it, we start to understand, why do they behave like this.
Of course, these novels have some drawbacks as well. The main one, in my opinion, is that narrative is too protracted. Some scenes are described too detailed, and some dialogues are way too long. Like, these things could be told much faster, without losing anything. It looks especially weird, when characters have a long monologues and thoughts in fight scenes. Also, I don't like that at some points narrative becomes too sweet melodramatic. Not a crucial drawback, though, since it doesn't happen too often.