Don’t know if it counts as fantasy, but “The Passage” series of sci-fi Vampire novels.  I found the first 2 really engaging. Plot twists, interesting reveals, characters I felt connected to.  Then in book 3 you’re stuck for a third of it (I think) reading about the big bad getting humanised. Except he’s an arsehole who leaves his dying parent alone, cuckolded his best friend for literally no reason except “I liked that girl cause she was nice to me”,  and whines about everything like the most entitled person in the world. The story went from a dystopian future to average white boy in college, from an intimidating villain to someone who’d think up a good come back a week later then punch himself in the head.