The book serves as a good tutorial covering the fundamentals of Mongo. It pretty well describes clustering (replicas and sharding) and recommended hierarchies but does not tell much about schema design and does not give you a hint of how to utilize the benefits of NoSQL databases like dynamic schema per document. The book serves as a very good tutorial, but there are several minor issues.
The book states that it is over 500 pages long, but actually, it is not that long. It has 24 chapters, there are a lot of empty pages at the end of chapters and parts and there are a lot of pages wasted by listing some command outputs. Most of them can be stripped significantly without affecting provided information. For example, there is command output starting at page 348 which spans over 5 full pages and actually only a few fields of this listing are referenced in explaining text.
I do not consider the book comprehensive. While it mentions a lot of things, the author does not provide extensive listings of features. For example, the book mentions how to use the operator plus, and they mention that other “common” operators work similarly, but they do not list them. To properly learn MongoDB, you will need to find them in the documentation. This happens to many other topics described in the book.
The book few times refers to terms which are not described at all or are only briefly described.
Lastly, I did not find data for experiments in Chapter 7 on GitHub and actually, it is the chapter which does the most complex queries against data.
To sum it up, it is a good book for learning MongoDB, but it most probably will not be your only learning material and there are a few mentioned minor issues, so I give it a 4-star rating.