Rebellion Against Society
The Phantom is in rebellion against society. His obsession with revenge is spurred by righteous anger borne from the conviction that society has rejected him. Like so many who become unwilling outcasts, he internalizes that rejection by rejecting his own identity and putting on the persona of the Phantom in the belief that without the masquerade, society would take no notice of him. Whether the Phantom is actually justified in feeling outrage at his ostracism is a key open question of the story.
Life is a Masquerade
A writer does not set his tale of gothic horror within the milieu of an opera house without taking on themes associated with reality, illusion, and perception. The plot focuses on seemingly impossible feats, overwhelming drama, and misdirection; in this sense, the entire novel becomes an exercise in arguing that most of what is experienced in life is an illusion to one degree or another.
Critique of Social Class
Like many other stories, The Phantom of the Opera engages the conventions of horror as a metaphor for the unfair results of social class and its rigid distinctions. The centerpiece of this theme is Moncharmin, who manages to become a director of the opera house despite having no musical training. Fortunately, Moncharmin possessed something deemed far more worthy: wealth and connections within the social elite of Paris. In a sense, Moncharmin represents a far more monstrous figure of evil than the Phantom.
Looks versus Talent
One theme found in the novel that seems to have never gone out of style is the propensity for those who look good to excel in competitions against more talented, but less aesthetically pleasing, rivals. Erik is unquestionably a great talent, but his dreams of fame and stardom are forever doomed by his disfigured face. Even today, this story is played out on a daily basis; for every Erik forced to become a Phantom because his talent goes unappreciated, there are a dozen, a hundred, or even thousand Kardashians. Given this reality, who wouldn’t go mad in the sewers?
The Duality of Obsesssion
Obsession is not inherently good or evil. When directed in a positive way, obsession results in the art of Van Gogh and the music of Beethoven. When directed in a negative way, the result is serial killers and billionaires like Donald Trump. Erik is not the only exemplar of this theme. While his obsession clearly gets away from him, consider the scene where the managers act obsessively to deny Erik his rightful payment. And, then, of course, there is the novel’s most iconic image of obsession, as portrayed on screen and stage: Christine’s obsessive need to view what lies beneath the Phantom’s mask.
Family
The importance and weight that Christine and Raoul give to their respective families could, arguably, not be more different. Whereas Christine is devastated when her father dies, almost giving up singing and performing, Raoul is quite content with arguing and publicly defying (via newspaper) his older brother, who has cared for him in the absence of their parents. At the end, Leroux does not indicate how Raoul reacted or felt when he heard about his brother's death - there is a strong degree of brattiness, apathy, and selfishness ingrained in Raoul's character. On the other hand, Erik ran away from his family at a young age, but for different reasons: his family could not bear his ugliness (as Leroux describes it); because of that, he chose to live a life as a drifter. Family has an incredible impact on the main characters of the story and the choices they make, particularly in the way they choose to value other people. Christine's loving upbringing leads her to become quite caring and compassionate herself; despite having a caring brother and lofty upbringing, Raoul does not act the same way; Erik, predictably is rash and childish, not having received much love or familial attention as a child.
Anger
With many emotions pervasive throughout the plot, we see that anger in particular is the cause of many smaller conflicts. This includes Richard's confrontation with Mme. Giry, when he accuses her of stealing money, yelling and seizing her wrist. We also see this with Erik, who threatens to blow up the Opera House if Christine does not marry him. It is also evident in Raoul, especially when he accuses Christine of deception and hurls a bevy of insults relating to a perceived lack of love on Christine's part. Though it may have been unintended by Leroux, the anger in the story is generally aimed towards women, and one woman in particular: Christine. Erik and Raoul's love and jealousy form the core of the plot, and Christine thus serves as a kind of proxy for their own desires and intentions (good and bad).
