Wuthering Heights by Emily Brontë is a Victorian novel, which traditionally contains characters who lead a hard and difficult life in nearly every way and are then redeemed in the end by hard work and overcoming, in some way, their personal flaws. In other words, in a Victorian novel, the protagonists spend the bulk of their stories enduring their difficult circumstances (usually created by some injustice(s) in society) and perhaps wallowing in their sinful natures, and are then rewarded for their efforts, ensuring a happy ending to the novel.
Wuthering Heights is significant because it is not a typical Victorian novel. One thing it does have in common with most other significant Victorian novels is that it deals with the distinct economic differences between the rich and the poor. That is the crux of Charles Dickens's A Christmas Carol, for example, and it is certainly an issue in Brontë's novel. In fact, this class distinction is one of the most significant factors in how things go for Heathcliff throughout the course of his life and this novel. In this way, Wuthering Heights is typical.
One of the ways this novel does not fit the norm, however, is that it is the only Victorian novel which places its characters outside the society in which they live. Of course the setting of this novel naturally isolates these characters, but they are additionally disconnected from a society that presumably does not matter much to them. In other words, society in this novel is seen only through the characters rather than as an entity which is as significant as any other character in the story.
That is not to say that society does not matter, as Catherine changes the course of both her life and Heathcliff's life based on her adherence to society's standards. She says,
"It would degrade me to marry Heathcliff now; so he shall never know how I love him; and that, not because he’s handsome, Nelly, but because he’s more myself than I am."
While Heathcliff is the man she genuinely and completely loves, her adherence to society's dictates destroys any chance for them to experience happiness. Even then, though, we see society through her eyes, not her through society's eyes.
Another way Wuthering Heights is unique is that it does not deal with social issues and problems like all the other Victorian novels. Instead, she concentrates on the inner workings of her characters' hearts and minds. She puts Heathcliff's rather violent emotions and feelings on display, and this focus on the inner workings of a man's soul is not something others were writing at this time. We are horrified by what things well up in Heathcliff's breast, but we connect to it, as well, because he is us.
Perhaps the most significant aspect of this Victorian novel is that it provides the first indication of the next thing to be written. It is a Gothic Romantic novel, containing many of the elements of the modern novel. The setting is haunting, dark, and mysterious, and the presence of ghosts and other supernatural elements certainly characterize the novel more as Gothic than as Victorian. Even more, Brontë's protagonist is moved to act more by the dark or evil side of his nature, another indication that this is a Gothic horror and more in the realm of Romantic than Victorian literature.
In short, Wuthering Heights distinguished itself both by being significantly different from nearly every other novel written during the Victorian period and by serving as a forerunner to the modern novel.