As a survey of Marxist thinking on cities, he does a pretty good job on a couple of thinkers I'm familiar with [Debord, Lefebvre], so I'm inclined to believe his summaries of other thinkers are just as good. Merrifield's book serves as an important reminder that Marxists thinkers have made important contributions in all fields including urbanism. This is hardly acknowledged except for Engels, who is still required reading in urban studies courses.
However, the author's own take on urban theory has limitations that mirrors those of his subjects: he is concerned with describing the contradictions within cities but does not consider the relationships between cities and the rest of the economy, nor between cities on an international level.
In his introduction, he dismisses third world socialists as "anti-urban" without seriously considering the impact that cities had on national [and in the third world's case, largely agricultural] economies. The impact had been that cities tended to monopolize resources, leaving the countrysides impoverished. This was, and still is, the pattern across various third world countries. Even today, in industrialized first world countries, in particular the US, our economies are dependent on a handful of large cities, which leads to my next criticism.
Neither Merrifield nor his subjects ever considers the effects of city size. One of the ways Maoist China attempted to equalize resources was to discourage the development of huge cities, and encourage the development of small- to medium-sized cities spread out all over the country. Merrifield never even questions whether it is desirable to have cities as large as Paris or New York. It would seem that Merrifield is not so much pro-urban as pro-megalopolis, but this is an approach shared by many otherwise insightful thinkers.
Since this book is concerned with charting the historical relationship between Marxism and urban theory, it can only briefly touch on new developments. For a look at some interesting new work, I would recommend that people keep up with Manuel Castells [no longer a Marxist I believe] and David Harvey, as well as Saskia Sassen [not a Marxist as far as I know but extremely insightful]. For all their differences, they all contain important insights which could lay a basis for a fruitful synthesis in the future.