i've only read a few dick novels. but the question of reality seems to be a recurring theme. the movie scanner darkly is pretty cool too. and of course, bladerunner is a classic of the genre.
Being an amphetamine addict will tend to make one question reality and become a tad paranoid Do Androids Dream of Electric Sheep is so much weirder than Bladerunner. Valis (based on his own experience of communion with an advanced being), Time Out of Joint, and The Man in the High Castle are my favourites. His novels often end abruptly with some arbitrary flying saucers, but that's the only way he could get them published in the pulp sci-fi magazines he wrote for. I recently found a copy of this: https://en.wikipedia.org/wiki/The_Exegesis_of_Philip_K._Dick which I've been wanting to read for years.
agreed on androids. crazy weird book. about ten years ago, the directors cut of "blade runner" was shown in an old movie house in chicago. i took my wife. she had never seen it. and she totally got that deckard was a replicant with no prompting from me.
http://www.slashfilm.com/man-in-the-high-castle-trailer/ a series adaptation of Philip K. Dick‘s novel The Man in the High Castle Coming to Amazon...
Sweet, I saw the pilot and presumed that they decided not to continue with the series. It's quite different from the book, but I think it has to be to work as a TV programme. I liked what they did with it.