Frankenstein because it's the first Gothic novel of the genre and maybe anything Mary Shelley and Carmilla because it's the first vampire novel so it just makes sense.
google lists interview with the vampire as a gothic horror book so i’m recommending it!! i love the book and if you’re a fan of vampire fiction then you should really read it!! also if you’re interested in queer fiction and how it interacts with vampire fiction then it’s incredibly interesting to look at within the history of queer vampire fiction. this is a bit of a side tangent, but it’s a topic i’m really fascinated with and love to talk about lmao :P