This novel was not what I was expecting given the jacket summary or the cover. It's pure, hilarious, laugh-out-loud satire--reminiscent of his Retief stories, but in my opinion more funny throughout. (The Retief stories were often funny satire at the beginning, then turned into so-so action-adventures, then back into great satire.) Also unlike the Retief stories, The Monitors is about the United States--slightly dated, now, since it was written in 1966, but most of the stuff he's making fun of is still quite recognizable today. It's not Cold War satire, by any means; all the attitudes here are still abundant today, and there's hardly anything about the particular political situation of that time (unlike, say, Dr. Strangelove).
It's pretty much equal-opportunity satire--just about every group gets its comeuppance. Democrat, Republican, lowbrow worker, hippie, professor, postmodern academic (yes, in a book written in 1966), militaristic conservative, do-gooder social worker, 12-step program, evangelist, even organized criminal. All the types are there (and some stereotypes, too--it does feel a lot like classic SF literature in that respect).
It's a great premise: somebody bloodlessly takes over the entire world, begins fixing everything that is unjust and wrong, and we just can't tolerate it, but for a whole variety of inconsistent and venial reasons. The Monitors begin to realize they don't quite understand what humans really are like.
All the action is pretty much spoof, not serious drama (even more so than a James Bond movie or the Retief novels; it's closer to Get Smart, but satirical). The main character is not a super-spy or a typical action hero, just an alert out-of-work, ornery ordinary guy who's trying to help save the human race, but is repeatedly thwarted by the comical foibles of the various resistance movements he encounters, or else just the preposterousness of the situation. For example, in one episode, he is running all day from various Monitor patrols, trying to ferry secret documents to the resistance. The ever noble Monitors finally catch up to him, and in good-neighborly fashion hand him the papers which he accidentally dropped hours ago, saying they've been trying for hours to find him to give them back.
So this is not a novel where the plot is supposed to be taken at all seriously. It will not keep you on the edge of your seat with suspense. But it might make you fall out of your seat laughing.