Far and away, my favourite of Philip K Dick's novels will always be "Do Androids Dream of Electric Sheep". I also really enjoyed "The Man in the High Castle", but predominantly, I've always preferred PKD's short stories. I find in some of the novels I've read, that the plots often begin to waver and the end don't always satisfy, but in the medium of the short story, Dick's satire is first rate, his pacing taut, and the imagination runs wild.

So the Zap Gun is a weird duck - it's not as good as the "great" PKD books I've read, but not as bad as the ones that left me cold (I really couldn't get into Ubik.) The plot (summarized adequately above and in the the other reviews) plays fair with the reader and the ending does have something interesting to say that actually ties into the human condition, the nature of empathy, and the protagonists' growth as a person - so those are all points in the book's favour - but there are quite a few places where the storytelling seems bloated - padding out an outstanding novella into an "okay" novel.

Still - worth a read.