I don't know if they're guilty pleasures but I enjoy some books that I see a lot of people hating on.

The Inheritance Cycle, by Christopher Paolini - LOVED those books and I don't care who says they're bad, I really liked reading them.

Dark Matter by Blake Crouch - loved this one too and only seem to see people saying it's boring.

Ready Player One - same as above. Really liked it and only see people talking about how it's bad or uninteresting.

Probably true guilty pleasure would be the Shopaholic books.