I've been a huge Blade Runner fan for years and this year I finally got around to read Philip K. Dicks Do Androids Dream Of Electric Sheep, the book that inspired, informed, and to be fair, is most of what Blade Runner is.
When I initially sat down with the book, I thought it would be the same universe, maybe some of the same characters, but that's all. I quickly understood, that the movie is, blondly put, a simple retelling of a book with changes that makes for a perhaps better story on the big screen. If you ignore the practicality of the differences, it's easy to imagine that the book and the movie is simply the differences that would exists between parallel universes, or maybe even when the same story is retold again and or again.
It's a great book, definitely a classic, but not as big of a deal as Blade Runner, which is a 10/10 on the recommendation scale, simply because while there exists lots of great contemporary books to this one, there aren't lots of great science-fiction, cyberpunk, neo-noir movies.