"Ragle Gumm is an ordinary man leading an ordinary suburban life, except that he makes his living by entering a newspaper contest every day -- and winning, every day. But he gradually begins to suspect that his world is an illusion, constructed around him for the express purpose of keeping him docile and happy. But if he is right, what is his real world like, and what is he actually doing every day when he thinks he is guessing 'Where Will The Little Green Man Be Next?'" -- from the back cover
Written in 1958 and published in 1959, Time Out of Joint (Dick's sixth published novel) explores a number of themes Dick had an abiding interest in, most specifically the nature of reality and the impact on people when reality as they understand it starts to unravel around them.
As with all PKD's works this novel makes you marvel at his imagination but also (if you are of a philosophical turn of mind) brings you to question and consider the themes he raises for yourself. PKD also creates characters that I at least find believable.
"[Dick] sees all the sparkling and terrifying possibilities. . . that other authors shy away from." --Paul Williams, Rolling Stone
"The most consistently brilliant SF writer in the world" --John Brunner
"Dick quietly produced serious fiction in a popular form and there can be no greater praise" --Michael Moorcock
"One of the most original practitioners writing any kind of fiction, Philip K. Dick made most of the European avant-guarde seem navel-gazers in a cul-de-sac" --Sunday Times
If you are new to Philip K Dick's work I would also recommend the following novels (which generally seem to be regarded as among his best):