This is a bold, visionary work with many merits. It also has one major flaw which makes it infuriating. First, the merits. Davis highlights the way contemporary urbanization has become largely detached from such processes as 'modernization' and 'industrialization'. Instead, rural residents have simply been pushed off their land by neoliberal policies, civil wars and such to the point where urban residents may constitute a majority of humanity (he does not consider at all the possibility that anyone may have chosen to move to the cities, either to escape constrictions on their choices of sexual partners, to exit family feuds, to seek opportunities, to party all night, etc). Cities in the global south are now mega-holding pens for the poor, sometimes, as in some Sub-Saharan African cities, without even a modest-sized middle class. The most rudimentary sanitation and health care is non-existent (Davis notes, early on, that some of the aspects of the city--pollution, industry, consumption--have migrated to the countryside as well, but he doesn't come back to this point). Slums are constantly being demolished and people are being uprooted as governments make way for permanent (shopping malls, condominiums) or temporary (Olympic games) encampments of wealthier people. He effectively debunks a number of romantic myths about slums--that they are self-organizing communities (they use subcontractors to construct their housing), that they are hotbeds of militant squatter movements (such movements are often coopted, creating a new strata of slightly privileged landowners), that they are filled with micro-capitalists (more slum dwellers work for petty capitalists than control their own enterprises). Instead, he produces the much less gratifying picture of myriad levels of petty exploitation, for example, by owners of slum housing of a renting population. It is a sober and disturbing picture, all the more so because he argues that previous beneficiaries of various nationalist and social democratic programs have become part of a privileged strata--which, at least in my mind, raised questions about whether programs can possibly be crafted that would not fall into this trap (there are other themes in the book--the limits of NGOs, the problems with IMF austerity measures--that are likely to be highly familiar to people who've read the radical literature on the global south of the last fifteen years).
Now for the infuriating part. The book is strictly a review of the literature produced by anthropologists, geographers, sociologists, novelists, etc writing about slums. There is virtually no firsthand observation in the entire text. I have no idea why this is. Surely as part of the research he visited some slums? As a result, slum dwellers almost never speak in the course of the book (I can think of two exceptions, one actually being a fictional character, the other drawn from someone else's ethnographic research). The book as a result lacks the humanistic grit that characterizes Davis' earlier work on LA and his more recent reporting on New Orleans.