I wish Kotkin had gotten more into the meta-analysis side of things rather than the historical summaries he provided, though those were well-written and useful.
Less dynamic and impactful than I'd hoped, especially the note Kotkin ends on -- is sacred space really so critical to the health of a city? His previous chapters didn't convince me, and the note about the critical element of urban growth being reliant on a "unified moral vision" raises more questions (and my dubious eyebrows) than Kotkin addresses.
This book's strengths are the ease in which it presents very condensed historical and geographical information in nice digestible sub-chapters, and its multicultural and global perspective. Some gems are scattered in here as well; names of famous architects and their influences, quotes about the definition of urban existence, etc.
Worth a read, but only especially recommended if you find yourself without a background survey of urban growth and want to acquire one.