I’ve only read one Colleen Hoover book (Layla) and I felt the same. It was very gripping despite not being anything special in terms of stylistic writing or unique plot/characters. Morally, the book was questionable, which I thought was interesting at the time, although now I find it a bit repulsive given what I’ve heard about some of her other books.

Mostly, I have to admit that she knows how to write an engaging story, and I personally think that’s how she’s so popular.