Despite it's popularity & high regard now, wasn't appreciated when published in 1847. Sold poorly.
Victorian readers shunned it for its 'inappropriate' depiction of cruelty & ungoverned love. Even Charlotte Bronte, who's novels contained similar motifis of Gothic theme and unusual/cruel characters found in Mr Rochester in Jane Eyre, adopted a cynical approach towards it claiming "Whether it is right or advisable to create beings like Heathcliff, I do not know. I scarcely think it is."
Concentrate on character of Heathcliff: complex & its our desire to understand him and his motivations be them psychological or physical that heighten the reader's levels of engagement in the novel.
Defies being understood.
Cliché of romantic literature, 'a reformed rake makes the best husband' - Bronte provokes the reader into questioning the possibility that Heathcliff is something other than what he seems. i.e. his vengeful cruelty is merely an expression of his oppressed love for Catherine or that his often evil behaviour is portrayed to mask a 'romantic hero' i.e Mr Darcy in pride & prejudice & Mr Rochester in Jane Eyre - traditionally romance heros appear dangerous & cold initially, until we understand this to be a concealment of their inner beauty, find them to be devoted husbands.
Heathcliff never reforms and his malevolence defines him as a person - almost like Satan himself, hence the references throughout the novel of Heathcliff as evil superficial creatures such as 'goblins' and 'devil'.
His sadistic infliction of abuse on Isabella Linton can be viewed as a representation of the reader's views on him.
Joyce Carol Oates - Bronte does the same thing to the reader that Heathcliff does to Isabella i.e. testing to see how many times we can be disgusted by his behaviour yet still insisting he is a romantic hero.
Romantic Byronic hero - all his passions destroy himself and others around him. self destructive - attribute of byronic hero.