As I post all of the books I read on Goodreads, I follow their star rating scale for my reviews. 5: It was amazing. 4: I really liked it. 3: I liked it. 2: It was okay. 1: I didn't like it.
Most books will fall into the 3 star rating. I can usually find the good in what I am reading, will be entertained or informed, and be able to recommend it to people looking for a similar read. If I enjoyed it enough to read it again, it will be a 4 star rating typically. I give 5 star rating very sparingly, reserving it for those books that resonated in my heart or mind. I will definitely read those books again, and rave about them to everyone.