Found the book to be a bag of mixed nuts in the sense that I have followed the "Observability" area for some time now so a lot of the content is not new to me.

But if you are looking for a good, easy to read introduction to "Observability" then this is a five star book. If you on the other hand are well-versed in the area then I would say it is a three star book, but there are useful chapters even if you have the basics in place.