Anno Dracula — Kim Newman. This is the vampire book to end all vampire books. No matter how creative you think you are, no matter how inventive you think your take on vampires is, I promise you that Kim Newman got there first.
The Black Company — Glenn Cook. Hands down the best dark fantasy novel of all time. All the dark, grim, “edgy” tropes that modern authors like to hang their hat on? Glenn did them 1980. In the space of a single book he created, perfected, and subverted the entire genre.
Catch-22 — Joseph Heller. One of the most effective anti-war books ever written, largely because it eschews maudlin tragedy porn and shows modern warfare for what it is: petty, mean spirited, and absurd.
vN — Madeline Ashby. One of the best robot books ever written, vN also represents (accidentally) one of the best representations of the trans experience ever written by a cis writer.
Whipping Girl — Julia Serano. This is a really excellent “intro to being a trans woman” book. I’m not 100% on board with everything (her definitions of gender are a bit fuzzy) but it’s a damn good primer to get you started if you want to know more about trans women.