It gets only three stars because there is not a whole lot to say on the subject so it is hard to say this is an awesome book. Coffeescript is pretty straight forward.
That said this book covers the language details really well and the flow of the book works nicely. I like how it displayed the generated javascript with walk throughs of what was going on.
The book also contains sections on NodeJS and Backbone. I only skimmed over this though. It would have been more valuable to me if the author spent more time on how you could combine some of the cool operators together to make things more readable and more succinct.