A.K.A. "zsh: the missing manual".
This book suffers from a single problem: it talks too much about shells that are not zsh. It tries to cover bash fairly well and has some exposition on csh, tcsh, ksh, which you're highly unlikely to be interested in, because the only reason you would get this book is Zsh.
That being said, it's a great book about Zsh. It incrementally introduces all the relevant features, without turning itself into a reference manual. I've been using Zsh for more than 10 years, and I definitely picked a lot of things from it (to name a few quick ones: SHORT_LOOPS, psvar + precmd, print -L).
The biggest value in this book for me is that it finally got me to start understanding the completion system, which is pretty complicated. I did end up writing a few completing functions and am now able to semi-debug other ones that don't quite do it for me.
The book is fairly old (2005), but as you can imagine, that's totally not a problem. New things have been added to Zsh, but it hasn't been majorly revamped or anything, so all the stuff there is pretty relevant. Obviously, it's not talking about oh-my-zsh or any of the 20+ plugin managers/configuration managers available today, nor it will give you any good ideas on how to do your dotfiles.
If you're looking for a way to casually configure your oh-my-zsh setup to be better, this book is probably not for you. But if you're a Zsh power user that ends up writing a fair amount of shell code, you can learn a lot.