A classic science fiction tale from the 40s. Slan has the obsession with ESP that most of the Science Fiction from that era has. It moves along rapidly like a novel fro, E. E. Doc Smith or from Bester. It is not quite as good as those and I did not like it as much as Voyage of the Space Beagle by van Vogt either.
Slan at the time it was written was considered a very important work in Science Fiction. It does not hold up in the same way, but one can see its influence on other writers. The hunted superhuman with ESP became a staple of the genre, and of course it is still alive today in things like X-men. Slan's date of being written in 1940 predates what was to become almost the most common type of book written in the 1940s and 1950s in science fiction. I myself do not really care for this kind of super-heroish storyline of the ubermensch, so it was only OK.
The psychology is not really there and there is next to no characterization. The flatness of the characters reminded me very much of Asimov. The book is OK. Its an entertaining read, but its decline in fortunes is somewhat deserved.