I follow the Goodreads rating model for all my book ratings.
1 star = I did not like the book
2 stars = It was ok – I liked some aspects of the book, but these were outweighed by aspects I didn’t like
3 stars = I liked it; 3 stars is a good rating – I enjoyed the book and would recommend to certain people, but there were a few things about it that I didn’t like
4 stars = I really liked just about everything about the book and would highly recommend it
5 stars = It was amazing; I don’t give many books 5 star. Reserved for my absolute favourite books that I will keep and possibly re-read