Because I'm a librarian, my ratings tend to be focused on how I would suggest books to customers based on what I liked and didn't like about the book.
Five Star: Absolutely loved and highly recommended.
Four Star: Very good. Certain people may enjoy this.
Three Star: Just okay. Not necessarily for me, but I know others who will like it more.
Two Star: Meh. Really didn't enjoy it but also something someone might like.
One Star: Couldn't finish the book and nothing could do it for me. Probably won't recommend.