PKD writes about my favorite topic which is how we perceive reality. What is real? Can we actually tell? I may need to read more of his books.
Sensation and Perception was my favorite class doing my Psychology major. Well, some days I say it was Tests and Measurements. (Probably the ones where I do something involving tests.) Let's call it a tie. S&P covers the mechanics and functionality of the senses, how the brain works with them, and best of all: how to exploit the failings of them.
The concept of an alternate reality where perhaps the Axis Powers won World War II found me intrigued. While what if realities are done quite a bit in science fiction, I enjoyed PKD's take. I especially liked the hinting at our reality in The Grasshopper Lies Heavy and slow unveiling of what it says.