Hmm. Most of my SF reading was early in life; I've only just circled back to it. Intro was Analog magazine, and juvenilia from Heinlein and Asimov. High-impact, in rough chronological order (of reading, not publishing): Foundation series: said that SF could tackle Big Ideas over Long Timelines. /
...same old social/political/cultural mistakes; or "how to keep the revolution going" (my takeaway, at any rate). Le Guin's the writer whose work spoke to me most powerfully, and shaped my thinking most. Fantasy... well, that's a whole other list and I still haven't had my coffee.
Dune: Added a level of complexity that was new to me at the time. Harlan Ellison (short stories): brought an intensity that I hadn't previously encountered. The Left Hand of Darkness: Blew my mind, had never considered gender previously. The Dispossessed: The difficulty of *not* repeating the /