I started reading Dick with Do Androids Dream of Electric Sheep and now five novels in have enjoyed every subsequent novel more than my first. This book is very much a Dick novel in that it is first and foremost concerned with personal identity. It is also concerned with the symbiotic relationship between criminals and the police.
It follows Bob Arctor who is an undercover police officer. As an undercover police officer he must take huge quantities of Substance D which causes roughly speaking split personality and psychosis. Arctor is eventually assigned to narc on himself and increasingly has difficulty understanding that Artor the police officer and Artor the drug user are the same person.
In addition to its interest in identity and policing the novel is also a spot on portrait/satire of what I might as well call the drug subculture. The whole picture is very disorienting and, like Arctor, we are not always sure what is happening. The novel is nominally a science fiction novel, but its science fiction elements are so turned down that it does not feel like one. It reminds me of Naked Lunch and also in strange ways of Vonnegut and even Nabakov.
Its arguably the best thing that I have read by Dick, although perhaps that is The Man in the High Castle. It is unusual fir Dick in that it does not really weaken or put a foot wrong and it is not uneven in strength. Very good novel.