With 45 published novels to his name, wading into the bibliography of Philip K. Dick can be daunting. When I first started, there were a handful of big titles I knew about, either because of a film adaptation or a major award they had won, but moving on after that became a series of trial and error.
EYE IN THE SKY (1957)
Dick's work is united around one theme, that being that reality can be shaped by an individual consciousness. Throughout his work characters question what is real, and whether the reality of the other people they meet is real. This book takes that basic premise as literally as possible An accident effects a group of characters where they find themselves in a reality shaped by one person's individual psyche. they try and escape each one, only to end up in another version. The book has some issues, I personally found Dick's portrayal of Islam to be problematic, but it is the first Dick novel that his ideas are expressed clearly, and entertainingly enough to be a must read.
TIME OUT OF JOINT (1959)
Most of Dick's work before this gem is pretty bad, even though it already contains the themes that he would explore later. This is the first "great" PKD novel. It deals with a man living a small town life, famous for his ability to consistently win a newspaper contest, and how he begins to question his reality. Many people have pointed out some similarities this book has to the acclaimed film The Truman Show, though with this book the premise is somewhat different. I think this book does it better, showing how we take the reality we are given for granted.
THE MAN IN THE HIGH CASTLE (1962)
The Man In The High Castle was Dick's only novel to win a Hugo Award, and it has become more famous because of the Amazon produced television series. It also is an early example of one of the most used alternative history stories, "What is the Axis won World War 2?" Still, the Dick novel is more than that. It examines the idea of whether the unfolding of history is inevitable, and what makes something real and what makes something fake. Despite the fact that the TV adaptation heavily features Nazis, they hardly factor into the book, which takes place in Japanese occupied San Francisco.
Martian Time-Slip (1964)
Martian Time-Slip is not as famous as many of Dick's other novels, but it does deal directly with a theme Dick dealt with in much of his work, mental illness. The main character is a repairman who immigrated to mars because he thought it would be better for his schizophrenia. While a lot of the psychological content involving schizophrenia and autism is outdated, this is still one of Dick's most interesting and entertaining works.
THE CRACK IN SPACE (1966)
I came across this Dick novel pretty late in my reading of his body of work because it is criminally underrated. In an overpopulated future America, a crack to another world is found. The world turns out to be inhabited by a race of less advanced people. The future president, who would become the first black man to take the office, can win the election if he advocates taking the land by force. The commentary on colonialism is fascinating, as are the racial politics, though Dick's portrayal of the native inhabitants leaves something to be desired.
NOW WAIT FOR LAST YEAR (1966)
This trippy Dick novel is a cult favorite, having to do with the idea of an addictive drug that appears to induce time travel. It is one of Dick's craziest novels, but it doesn't go off the rails like many of the books he cranked out have a tendency to do. It's a good look at Dick's themes of drugs, addiction, paranoia, and insanity.
DO ANDROIDS DREAM OF ELECTRIC SHEEP (1968)
This book is one of Dick's most famous, because the film Blade Runner is adapted from it. It is common to hear people say they prefer the film, but the movie version tones down many of the books most compelling themes. When animals become almost extinct, and intelligent androids provide free labor, the human race shifts its ideas about what it means to be human. Dick asks this question in a provocative way, and explores his usual theme of authenticity.
If I have to choose one Dick novel as the "quintessential" Dick work then I have to go with Ubik. It has alternate realities, seeming time travel, philosophy, religion, and enough trippy ideas to keep you guessing what is real and what isn't. In fact, this is the Dick novel that will make you most feel as if you are on a mind altering drug. That is the biggest compliment I can give it. I hesitate to say anything about the plot, except that it involves a spray product that might be the key to understanding the universe.
A Maze of Death (1970)
If you imagine a sci-fi version of Agatha Christie's "Ten Little Indians" you will get an idea of what this book is like. A rag tag group of people end up on a deserted planet and start getting killed off one at a time. This book is tightly constructed for a Dick novel, sticking mostly to the plot, but there is a lot of hilarious satire and religious ideas thrown around to keep things interesting.
Flow My Tears, the Policeman Said (1974)
The ending of this Dick work is polarizing, but I think it works just fine. Other people accuse it of being lazy writing. The story concerns a celebrity who wakes up in a world where he isn't rich and famous, and is a nightmarish dystopia to boot. One of Dick's more interesting journeys to alternate realities, this one keeping the focus on character and philosophical musings rather than conventional plotting.
Confessions of a Crap Artist (1975)
This is the only one of Dick's "literary novels" to be published in his lifetime. It was written much earlier than its publication date, and in my opinion is the only straight Dick novel that is a "must read." The title character is a paranoid conspiracy theorist war veteran, but Dick's genius is in contrasting the worldview of this seemingly mentally ill character with that of the seemingly sane people around him. Dick's ideas about personal realities is made accessible without relying on a sci-fi premise.
A Scanner Darkly (1977)
This book is a potent commentary on the war on drugs, told with a mature nuance that shows us where Dick might have gone if he had lived longer. An undercover cop consumes the drug "substance D" as part of his investigations, but the drug causes him to develop a "split brain" and his cop personality and undercover personality become separate, causing him to investigate himself without knowing it.
Late in his life, Dick received a series of religious visions that he struggled to understand. This led to him writing several novels that directly addressed these experiences. The best of these novels is Valis, which explores Dick's theme of mental illness in a strange religious context. An intelligent satellite is sending "Horselover Fat" strange visions, and his friends, including the author Dick himself, try to help him figure out if he is indeed insane.
Radio Free Albermuth (1985)
Before completing Valis, Dick took another entirely different run at the novel. Not thinking this novel was adequate, he ended up shelving it and working on Valis, though the plot of this novel appears in that book as a drive-in movie the characters are watching. The plot is roughly the same, only this time taking place in a dystopian alternate reality. Dick even appears as a character in this book as well, though in a different context. Dick's shelving of this novel is somewhat puzzling. It is better than most of his books, and the plot is different enough, while following the same themes as Valis, for them to function as two completely separate novels.