For me, the most recent book regret is Dark Matter by Blake Crouch. Predictable from the get-go, bland, boilerplate sci-fi ideas, too many of these way-too-convenient plot devices just to push the story forward. I frankly don’t get the hype, and I am a pretty big science fiction guy.
Another one is Blink by Malcolm Gladwell. I read this in college and this whole book should have been a one-page essay. It was too repetitive, and the whole premise of “trust in your snap judgments and gut reactions” is way too simplistic and honestly stupid. Like all Gladwell books, it was anecdotal, superficial, and a waste of time.
I regret finishing the Malazan series; I liked the world building but none of the characters felt real and the ending wasn’t worth it. Same issue with Dune but I gave up halfway through Children of Dune so I don’t regret it as much