Forbidden Area is more of the same. It was published a few years before Alas, Babylon and is not quite as good a novel. In this book, the Soviet Union has planted sleeper agents in the U.S., with a sabotage plan that will make possible the conquest of America by nuclear weapons. One of the characters in the book at one point asks what on earth they would want with a continent covered with radioactive waste. "Maybe they'll just put a fence around it with a sign saying 'Forbidden Area'," is the answer.
This isn't a very long book, but I felt at time that I was never going to finish it. There are a lot of characters, few of whom have particularly distinct personalities, and eventually I just gave up on keeping most of them straight. (It's pretty clear what the role of each character is, anyway, so I just treated them as though I was meeting them for the first time whenever I encountered the name. It didn't really matter, in terms of understanding the book.)
I was in elementary school during the '50's and '60's, and I found this book to be pretty indicative of the attitudes of the time. I had pretty much forgotten how frightened we were of the USSR in those days, but this brought it all back. It's an interesting look at a slice of the past, and I recommend it for historical perspective if nothing else. As a literary piece, it leaves a lot to be desired.