Part of the reason for the great success of The Phantom of the Opera is that it came at a time when there was a wave of interest in horror in general and vampires in particular. Although he is no blood-drinker, the Phantom closely resembles the threatening yet elegant vampire of modern fiction, an idea which began with the recasting of older legends by Bram Stoker in Dracula.
Also, The Phantom of the Opera is, like My Fair Lady—with which Webber compares his work—a romantic story. In the case of Phantom, the story also resonates with the complicated relationship between husband and composer Andrew Lloyd Webber and wife and singer Sarah Brightman, that, some time later, ended in divorce.
Phantom should be compared to My Fair Lady for a better reason: It, too, is a variation on the myth of Pygmalion and Galatea. Indeed, George Bernard Shaw named the play which was used as material for My Fair Lady, Pygmalion, and it, unlike the musical derived from it, could not be mistaken for a romance between the creator and the created.
Liza, we are told in an afterword, marries Freddy, and it takes time and money before the pair of them become successful business people, running a flower shop. The musical ends with Higgins calling to the returned Eliza, "Bring me my slippers," which most members of the audience chose to take as evidence of a romantic attachment, but Lerner and Loew, knowing the source material, deliberately made the ending ambiguous.
For Shaw, the outcome was obvious, and he sums up his analysis of what would happen thus, "[Eliza] likes Freddy and she likes the Colonel; and she does not like Higgins and Mr. Doolittle. Galatea never does quite like Pygmalion: his relation to her is too godlike to be altogether agreeable." Perhaps the Angel of Music was doomed from the beginning to lose his creation, Christine's singing career, which she gives up without a backward glance to become a wife and a mother.
One final note: Although Andrew Lloyd Webber has been successful with several quite different lyricists, his great strength lies, not in his music, but in the skills of an impresario. He can draw forth astounding results from the many kinds of people needed to make a stage production. In the very end, I suspect that he and whoever writes the words for his musicals may never reach the heights of a show where the song critics thought the weakest begins, "I have often walked down this street before..."