Isaac Asimov's SECOND FOUNDATION is the third volume of a trilogy that has earned "landmark" status as truly definitional to a genre. The genre, of course, is science fiction, or in its slightly hurt nickname, "speculative fiction." as Nabokov said, any exact definition of "sci-fi" would have to include Shakespeare's Tempest (ca. 1610), but that's a distinction most literary scholars would be loathe to make.
I disagree with Nabokov. SF, I feel, must include the development of technologies that alter human society. To that end, jules Verne qualifies with his endlessly powered undersea or outer space journeys, but Apuleius with his mystical transformations does not. Margaret Atwood clearly has written SF (among other, literary works), but Hunger Games is probably young adult adventure in a speculative universe. I agree the line can never be made absolute, but "Hardboiled Wonderland" doesn't seem sci-fi in the way Ballard does. Martian Chronicles is firmly genre, whereas F451 sits just uneasily outside.
Its the "science" that is critical, I feel. And Second Foundation (2F) clearly serves as "archetype" of the genre, even as it mirrors much of the pulps that characterize golden age comics and SF. 2F covers the sweep of galactic history, with an undertone that Nietzsche would have understood, but it contains also a PKD moment of dueling psionics, and a little bit of the "large pink exposed aliens" sort of feel, which might be a point against. That said, clearly technology and science have altered the human realm, so that degree, this is classical skiffy rather than spec fic.
The final question, of course, is, "are science fiction nerds geeks and losers?" well... I' m not rushing to meet Jonathan Lethem, the most literary of the sci fi geeks, but I wouldn't necessarily turn down dinner with Ursula le guin nor would I necessarily value a speech by Ian mcewan over a lecture by William Gibson. So in the end I guess its all a blur, Neal Stephenson over david guterson. Wel.... Check out myers' 2003 "readers manifesto" for more fun and games
"decline and fall of the galactic empire", this trilogy is a landmark. Final volume, 4/5, but series overall 4.7 and distinctive