An adjective, meaning "characteristic in feel to a Philip K. Dick novel."
Similar to the term "Kafkaesque" (which refers to Franz Kafka) both in usage and meaning. A dickian experience is one in which you are nagged by certain doubts; these can range from doubts of the authenticity of a historical artifact to doubts about the fundamental aspects of existence: the nature of your identity, the nature of your humanity or of humanity in general, and most commonly, the nature of reality itself.
The term can also apply to Dick's particular way of writing, especially word-useage-wise. (Appending the word "wise" to a gerund to yield an adjective is a particularly common aspect of dickian writing.) Dick also has an abiding affection for the word "ersatz." (thanks to dTaylorSingletary for pointing this one out)