I was glad when I got to the appendices when only about 60% through the book, as then I could stop. That's not a good sign. The book is very long and jumps off into all sorts of random directions.  
On the other hand, it is an interesting topic and he does provide a lot of interesting details. 
I do think that he exaggerates the role of his two central characters,  as well as being overly US-centric.
The dichotomy between the two schools of thought works better in some parts of the book than others. For instance, I didn't find it convincing when applied to solar power as that technology is implemented both in an industrial centralised way and on individual households. 
As a small point, the figures about photosynthetic efficiency are wildly out. He states 0.00025% whereas it is actually about 2%. 
He writes about how governments for water services provide 'very inefficient services providing very bad service'. This was clearly written before the debacle of privatised water services in the UK.
Another thing that came after the book was published has been the substantial shift to sustainable energy in Europe. That has clearly gone faster and further than he imagined. That has happened not only because of altruism for future generations (it doesn't seem to have occurred to Mann that people care for their children and grandchildren) but due to government policy shaping economics. 
Like most writers who mention the relatively short time methane stays in the atmosphere,  he neglects to say that it degrades to carbon dioxide,  so its effects continue.
I enjoyed the chapter about Wilberforce and Huxley, that had some new insights for me.
In summary,  an interesting book, but it would have been better if better edited.