Very strong. Narrative develops organically and dialectically out of prior installments. Principal villain, to the extent that there is a villain, likewise develops organically from the events of the third volume. Plato’s forms deployed as weaponry and counter-weaponry. Conclusion is satisfying.
Primary conflict places proponents of industrial development against irredentist true believers in platonist magickes. That these two essentially economic theses are represented respectively by the two principal characters of the entire series makes for effective narration. By the end, what is solid, in pertinent part, literally melts into air. Good stuff.
Is something of a fantasy of biopolitical management, which is hinted at in Scott Bakker and made explicit in Brunner’s [b:Stand on Zanzibar|41069|Stand on Zanzibar|John Brunner|http://d202m5krfqbpi5.cloudfront.net/books/1360613921s/41069.jpg|2184253], in which the primary motivation is the pressure of depopulation or overpopulation, and how the state handles the glut or dearth or whatever. Will need to cogitate on that a bit more, but this text is certainly front & center in an inchoate subgenre of demographic fantasy (or would it be demological? demonomic?).