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.
Star Wars Black Fleet Crisis Trilogy. Most Star Wars novels are actually pretty good, but this trilogy was very disappointing, and I wish I would’ve just DNF’d it. Honorary mention to The Kill Order, basically the exact same plot as Star Wars Rouge One and Halo Reach, except not pulled off nearly as well.