I recently took a look at my book reviews and noticed that the last one that I received was a one star review. My book is not for everyone and I understand that. While disheartened, I know that some people may want more information.
This reviewer was looking for more in depth information and possible some metrics. That is good feedback for a follow up book.
Make that that you are encouraging feedback, good and bad. It helps you grow personally and professionally. The feedback can help you improve or keep doing what you are doing.