The authors, Steven Levitt and Stephen Dubner, describe Freakonomics as "whatever freakish curiosities may occur to us." The book has little to do with economic analysis. It has little to do with analysis at all: analysis is used just so far as to provide a "Gee Wiz" type of answer, which is rarely considered deeply enough to provide real insight.
For example, the case study of three little girls (presumably around 8). The parents of one girl will let her go to visit one of her friends, who has a swimming pool, but not the other girl, whose parents have a gun. The authors provide the statistic that more children under 10 die of drowning in backyard pools than die in gun accidents so presto besto - the parents are irrational. But the parents are not dealing with average children under 10 - they're dealing with a specific set of circumstances. If most children who die in backyard pools are toddlers or older children who don't know how to swim, and if their 8-year old knows how to swim, then the swimming pool death statistic isn't relevant. For authors who claim to be trying to "understand the hidden side of everything", they seem to be more interested in taking cheap shots at the conventional wisdom than providing real insight.
Similarly with a chapter on how rich or educated people name their children vs poor or uneducated children: a 25-page chapter yields one insight, that the most popular names for poor or uneducated people are sometimes the names that rich or educated people named their children ten years before. That's it.
The chapter on crime is confused. Levitt's one original insight, that legalized abortion was a contributing factor to lower crime rates, is pretty neat. But the rest of the analysis is a mishmash of other theories, poorly and inconsistently explained. For example, they go back and forth on the importance of having two parents, and they don't even seem to notice they're doing it. There is no thought given to the different types of single-parent households: were the parents ever married; is the father around or paying support; has the child met the father. They make some startling assumptions, such as that sending more people to prison decreases crime rates, while Canadian studies show just the opposite - and at one point, they even argue the opposite (that increased jail time enabled gang members to get to know drug importers).
I like the repeated appeals to stop confusing correlation with causation. The book starts out well, and the first 100 pages are the best, but the whole thing is less than 200 pages, with the last half seeming a lot like filler. (My edition came with some "bonus material" - an overly laudatory bio of the authors and some previously-published articles that partly duplicate the material in the book.)
One of Levitt's recurring themes is that so-called experts often have their own agendas and so we should be wary of trusting them. That's an unintentionally self-referential argument. This book reads like a thrown-together rehash of old material, inadequately considered, with a hyped-up meaningless title, designed for one purpose - to make some quick cash. A more thoughtful and well-argued book might not have had the same mass appeal.