I've been working my way through the code samples. As expected, there are a few places where the code has editing/syntax errors, there are a few places were the code works but it does not do much to improve understanding (and could be improved to make it crystal clear) and there are a few places where Backbone.js has since changed since the book was published. The Backbone.js basics chapter is long but, in several cases, glosses over important topics, especially the Backbone.js REST support. Through trial-and-error and continued reading, I have gotten to understand them but I would have preferred the book to explain them thoroughly and in one place. The Backbone.js basics chapter is tough and tedious to work through and required several attempts. It is tough and tedious because I am actually typing and executing the code and, due to the errors, lack of clarity and Backbone.js changes, I need to spend 1/2 hour to enhance and experiment with the code every 1/3 of a page.
The two Backbone.js chapters with sample applications (a To Do list and a Library) are significantly easier and a bit better than the Backbone.js basics chapter and the Library sample goes into more detail about Backbone.js REST support. Still, the book would have been better if it had done a line-by-line explanation instead of just summarizing and glossing over details. It's a missed opportunity: rather than dissect Backbone.js for all to see and nail down the details once and for all, the book settles for drive-by explanations.
The Marionette and Thorax chapter is written with co-authors. They read like blog posts and are completely disconnected from the previous chapters. The Marionette part is difficult and full of unexplained code but almost understandable. The Thorax part is only 6.5 pages and largely incoherent. This chapter is filler.
I'm not done with the book; I'll try to remember to update my view when and if I finish.
Despite what I've said, I recommend the book because it is helping me to learn Backbone.js.