I think this must have been the last book Blish published in his life-time. It says that Star Treks 1-10 total 6.5 million books printed which is interesting in that over 40 years later it's not these that are still in print, but rather a half dozen or so very influential SF novels straight from his own imagination that show a fascination with Catholic theology, James Joyce and shock endings, among other things.
It feels like the later members of this series of adaptations of the original Star Trek shooting scripts suffered from being essentially the dregs; the best had all been used earlier. Here several of the stories make no sense at all and one of them ends with a hideous cop-out deus ex machina - but blame the script writers, not Blish!
This is the first of the Cities in Flight novels by time of setting but the second in order of writing. The only other work I've read by Blish is the far superior A Case of Conscience. This book is written in a style like Heinlein's but it reminds me very much of the Foundation series by Asimov, which I don't necessarily consider a good thing. There is far too much standing around talking and the great mystery that is reveled is something that you know is coming.
However, Blish is talented enough that I want to give more in the series a go. Not exactly a bad book, but a little disappointing.