VALIS, by Philip K. Dick
I can't decide if this book is brilliant or utterly ridiculous; perhaps it's a bit of both. It's incredibly hard to explain "VALIS," but here goes: Dick, writing about himself in the third person as Horselover Fat, has a psychotic break. He thinks that God/Jesus/Buddha/Asklepios/an omniscient alien satellite fires a beam of pink light into his head and he is suddenly filled with knowledge, both of a mundane and surreal nature. Half the book is taken up with Fat's exegesis, delving into the mythological pasts of most of the world's major religions, conflating and explaining them. The rest of the story is actual plot, though even most of this consists of philosophical/religious discussions amongst Fat and his three friends (one of whom is Dick, who at this time considers himself a totally separate entity from Fat). Since I studied history and religion in college, I was able to follow a good deal of the exegesis, but it was still confusing and hard to get through at parts. I'm still trying to sort out exactly what it is I read... This is probably the least accessible work of science fiction I've ever read, though interesting, and I'm glad I read it despite not understanding it all.