Off the top of my head when it comes to the genres I read the most:
-The Girl with the Dragon Tattoo. The nordic thriller genre was highly prolific well before it, at least since the 1960s, but Larsson popularised it to a wider non-Nordic public by introducing cartoonish, exaggerated, violent, movie-like elements that contrasted with the tradition both of Nordic thrillers and of crime novels in general, and formed the basis for many successful writers that came afterwards.
-Battle Royale. Pulp, extreme and theatrical, it is a landmark of dystopian fiction that IMHO deserves to be in the same realm as 1984 and Lord of the Flies (not necessarily in prose quality, but part of it is because it’s not in English originally and the translation is bad) and is perhaps the single most important work of the whole “killing game” sub-genre.
Hilary Mantel CHANGED THE GAME for historical fiction. Her books were so well researched they might not even be considered fiction, and her writing was so powerful that she changed it from ‘genre fiction’ to literary fiction. I don’t think we’ve seen that since The Leopard.