Overall, the book was ok. Defintely not what I was expecting (according to the references of Gabe Zichermann), the holy grail of gamification.

In general the book presents a lot of case studies in favor of gamification and gives a couple of guidelines about how to make gamification work. I could argue, that in some cases, examples of real games are given as gamification examples (ex: Foldit is a game in its own right, not a gamified app).

I was also hoping to find a structured implementation plan (like in For the win, also a book about gamification), but I was left hoping.

To sum up, you're better off watching the talks that Gabe gives than reading this book. You will probably learn more about gamification that way.

Later edit: While working on a scientific paper I started checking the references that Zichermann uses to argue pro games at the beginning of the book. I am utterly disappointed in how he used the numbers that only favors his argument.

I will give the two examples that I've checked (I stopped after that because I lost credibility entirely):

1) "From 2002 to 2012, the Census Bureau estimated that the total time playing video games doubled in the U.S. adult population. Furthermore, this data is likely to vastly under-report actual game usage: it excludes children 12 and younger, and it most likely also misses social and mobile players who don’t think of themselves as gamers (but nonetheless play games)."
This is where he got the data: www.statista.com/statistics/186960/time-spent-with-videogames-in-the-us-since-2002/ (if you make a free account you will have full access to the page).
Anyway, notice the two footnotes:
Estimates for time spent were derived using consumer purchase data.
* Values for 2009 to 2012 are projections.
To say "this data is likely to vastly under-report actual game usage" under these circumstance seems a "bit" far fetched.

2) Casual game leader PopCap commissioned a study in late 2010, and the study revealed something that many women could have told you: the average gamer is no longer a 13- to 34-year-old male. She is a 43-year-old woman.
This is where he got the data: www.infosolutionsgroup.com/2010_PopCap_Social_Gaming_Research_Results.pdf
My doubts: why use the data from 2010? The statements is made about social gamers, not the average gamer (whatever that means).