I have two. The Ritual and Drowning.
The Ritual is pure smut. 61 chapters and every one contains a graphic, demeaning sex scene. I’m convinced the author was an adult film screenwriter and decided to try their hand at writing a novel. There isn’t a single likable character in this book.
Drowning isn’t a great work of literature. I felt that the characters were very two-dimensional. I hated how naive the author made the protagonist. It made me have a lack of sympathy for her. The ending was series finale of Dexter bad.
Thrawn: Alliances (2nd in Timothy Zahn’s Thrawn Trilogy). The first and third books were excellent, but this one was just Anakin, Padme and Thrawn traipsing about on some backwater planet. It was boring, especially since everyone already knows how Anakin/Padme’s story ends. I sat there through the whole thing thinking “none of this matters.”