Here are the definitions for star ratings for my book reviews:
***** An original work, masterpiece, must-read book.
**** Very good book with a lot of interesting insight, useful & enriching experience. This is the book you just can’t put down.
*** Satisfactory experience, several good ideas and not too many cliches, worth reading if you have a lot of free time.
** Either poorly written book or an obvious copy-paste full of common knowledge for the area.
* Very poorly written book, complete waste of time. Something that I normally wouldn’t review as just skimming through the book reveals that.