PKD is my favorite author of all time. A Scanner Darkly is my favorite work by him. The themes of the consequences of drug use and the loss of identity/self spoke to me on many levels when I first came across the work many years ago. I started out with the movie and read the book later in life and was pleased how well the movie adapted the novel. It never pushes onto you any anti or pro drug narrative on you and has a powerful ending(IMHO). I know loss of identity and self is somewhat of a trope in scifi but it just felt different with A Scanner Darkly. It was more profound. It may have to do with the fact I was introduced to it as a teenager and it was a very common thing for teenagers to question who they are as a person. I was a very heavy drug user at the time as well during the time. But… I don't know really. When I revisited the work later on in life and read the novel it still spoke to me.
Now Flow My Tears, The Policeman Said was all about a man losing his identity. The tragic story of a famous star losing everything he ever had in life in a society that had strict laws on having your identity in the system. He goes on the run in this new alternative reality because it's going to be discovered he is a man with no identity and the government will hunt him down. I don't know if I could explain the book further without spoiling much, but it's a very fun read. I would love to see a movie adaption of the novel(if there isn't one already that I'm not aware of).
Ubik is amazing. I'm a big PKD fan and have read a bunch of his stuff but Ubik still stands out as the best. Also made me have very beautiful and thrilling dreams, often I would wake up in a trance or with an adrenaline rush.