This is an outstanding book. It contains only suitable material for its intended age group. You may want a print copy for your bookshelf, and you may buy one for a friend.
This is an excellent book. It doesn’t quite rate five stars (for the reasons stated), but it’s perfect for its intended age group. You will probably re-read it, and you will recommend it to friends.
This book is average. It’s a decent read, but you probably won’t read it again. If someone asks, you will admit that you read it, but you might give your friend the low-down about either the writing or the content.
This book is not recommended, either due to poor writing quality or objectionable content (or both). You are sorry you spent the time, and you will warn your friends.
This is a poor excuse for a book. You may rant about it to random strangers.