Much like Freakonomics, Superfreakonomics is an entertaining book that covers a wide variety of unrelated topics in a fun way. But in contrast with Freakonomics, it is less reliant on econometric analysis and more on anecdotal evidence. As a result, its conclusions should be taken with a grain of salt.

For example, their finding that it is safer to drive than walk while drunk depends on several assumptions that may not hold. One such assumption is that the level of inebriation is on average the same for both drunk walkers and drunk drivers whereas, as they point out themselves earlier in the section, most people believe it is safer to walk when drunk, indicating that those who walk while drunk are probably more inebriated than those who drive while drunk. But to put things in context, that was just a small example and is only a very minor part of the book.

Sadly, many critics and reviewers are basing their entire opinion of the book on the last chapter concerning global warming. Let me just point out that it is not true that they are claiming that global warming is not a problem. Yes, they do mention some old global cooling theories from the 70's. But put this in the context of this book - a random collection of fun facts - and you can see why such theories were mentioned.
But that misses the main point of the chapter. In fact, the purpose of the chapter is to find a way to cool the globe, but using geoengineering, as opposed to restricting emissions of Carbon Dioxide. They propose an idea sponsored by Intellectual Ventures, a company whose business is to accumulate patents in a wide range of fields. The plan basically entails the injection of sulfur dioxide into the stratosphere, which would reflect sunlight and possibly cool the Earth. The authors propose this as a much cheaper and possibly effective solution for global warming.
You can see why environmentalists may be annoyed by this book: it gives their political opponents some ammunition in a critical time when they are trying to pass environmental regulation. It is thus critical, for them, to destroy the credibility of the book and its authors. Perhaps this is an understandable position, but the attacks on this chapter of the book are highly unwarranted in any other context given that it is merely proposing new ideas, and there's nothing wrong with that. For all we know, more research could prove that such schemes are effective.

Buy this book if you enjoy reading a collection of fun, often counter-intuitive, random "facts" about controversial issues. I would give it 5 stars for entertainment value, but I only gave it 4 stars out of 5 because the high level of econometric analysis that could be found in Freakonomics is virtually non-existent here, making the sequel sloppy and less rigorous.