I read a lot. I enjoy writing and saying things about books. I use GoodReads, Kindle and Audible.com. I like to rate the books I read. I have always had a fairly rigorous idea of how I use the usual five-star rating but, was trying to decide if four stars was right and realized that it would be helpful if I could consult a standard to decide. Here is mine.
Five stars is reserved for books that are life-changing and superb. Five star books will be amazingly well-written and incredibly interesting. This is rarely given by me but, when I finish a book and truly wish I could stay in it forever or that my perspective on something has been substantially improved, this is where it goes. Five star books are transcendental, wonderful experiences. If you share anything with my views, I believe you will love this book.
Four stars indicates that I really like this book and that I think you should read it. It will be, in my opinion, very well written and interesting. There will be things about it that are unique and present new ideas. Characters, plot, and other mechanics of writing will be very good. These are books that I recommend enthusiastically and that I am sure I will bring up in conversation fairly often. Four star books will leave you feeling satisfied and wishing for the book to never end.
Three stars is for a good book that I think you will enjoy. I am an easy-going person and do not require an author or a book to be perfect. I am happy to overlook flaws in a book if it has some good ideas or is just a pleasant way to while away the hours. I believe that a three star book will please you and that you will feel that the time it took to read was well spent. In my world, Three stars is a positive rating.
Two stars is for decent books that I didn't like very much. My dislike might stem from feeling like the viewpoints are annoying or the mechanics of the book were too evident and distracting. If I'm bored by a book that has an interesting premise that I can imagine others would enjoy, it might get two stars from me. Two star books are ones that someone who shares my views will not be likely to enjoy.
One star is reserved for books that I hate. If I give a book a single star, I probably did not finish it (though I have a 'hundred page rule' so I am never capricious in abandoning a book) because it was so boring or stupid that I felt insulted. In my opinion, a book with one star is a book that is worth neither the time or money it will consume. When I give a book One star, it's because I am fairly irritated that the author would foist this kind of crap on me.