I always tend to have a bit of a depression everytime I finish a book that I was invested in. But in particular, White Fang by Jack London left me in shambles
I had a similar, but opposite experience. I got very into The Three Body Problem. The Dark Forest was good, but not really my cup of tea, but I'd heard such good things I carried on. I did not like Death's End one bit and was really trying to slog through but threw in the towel half way through, looking for something light and fun and magical to cleanse the palate after that gory depression fest. I picked up The Color of Magic by Terry Pratchett (delightful) and didn't read any sci-fi for a year or so.
There were a few in Asimov's later science fiction books. The Naked Sun to Robots of Dawn made me want to read more of what happened after the zeroth law - a sometimes fun thing to play with in conversation with AI too. It usually finds amusement in the concept.