I'm writing a MA thesis on monstrosity in British gothic literature, and Frankenstein is one of the works I'm analysing. I've gotta say, I rather liked it. Indeed, it was not the creature but the creator who was the monster. The creature's ugliness was a reflection of Victor Frankenstein's hidden obsessions and fears. You could say that the creature was its creator's alter-ego.

@Milady Purity: Frankenstein came first, in 1818. Phantom of the Opera was first published in 1909-1910.