It's cliche I suppose, but 1984 by Orwell. It's actually a fucking great read beyond it's thematic meaning. People are correct in saying A Brave New World was more prescient, but it's not as good a book in my opinion.
Joe Abercrombie's The First Law series, all six mainline books and even the side books are all fantastic.
It's manga, but Berserk by Kentaro Miura. IYKYK
I read Frankenstein in my highschool literature class way back, loved it then and love it now. Shelly was a pioneer.