Buffy the Vampire Slayer
Joss Whedon's high school horror riff did something television had not managed before: it took the dumbest possible premise, a cheerleader kills vampires, and used it as scaffolding for the most literate genre drama of its era. Buffy Summers moves to Sunnydale, a town built on a Hellmouth, and over seven seasons the show treats every monster as a metaphor for something real: first love that literally leaves a scar, the person you sleep with turning into a monster after, a mother's death that no slayer strength can fix. The gimmick was monsters, the subject was growing up.