Vampires have always had this strange cultural magnetism for me, maybe because they're the ultimate outsider figure, even among monsters. They move through human society but can't truly be part of it. I think what sets them apart is the unique blend of personal horror and existential dread.
I just finished a re-read of 'Interview with the Vampire' and it struck me again how the best vampire stories aren't really about the powers or the violence. They're about the cost of immortality—watching everyone you love decay while you're frozen. That's a kind of supernatural torment ghosts or werewolves can't really touch. The classic tragic, romantic vampire works because he's a prisoner of his own endless existence, a predator burdened with a human conscience he shouldn't have.
Also, they've evolved so much. Anne Rice made them introspective and glamorous, but now you get stuff like the vampire bureaucrats in 'What We Do in the Shadows', or the gritty, disease-like vampires in 'The Strain'. They're flexible enough to be monsters, lovers, heroes, or a dark reflection of human excess. Maybe it's that flexibility that keeps them fresh.