As a kid I absolutely hated when book covers of illustrated books would be paintings of the kids in the book which looked absolutely nothing like the book illustrations of the same kids. This was particularly common with paperback editions of kids' books back in the day, like some older editions of the Ramona Quimby books, Harriet the Spy, etc. Why not just use the book illustrations on the cover?

More recently, I have basically stopped reading books with the cover image of a woman in old-fashioned clothes with her face obscured. Just way overdone. And I'm almost at the same spot with the colorful abstract collage-style designs covers. Enough already, publishers!

On the other hand, I love book covers that utilize cutouts in their design. I'm convinced that a good portion of the reason V.C. Andrews's books got so much attention back in the day was those eye-catching cutout covers. I also remember when The Secret History came out with that opaque cover overlay -- really brilliant design work.