The best answer is included elements of mystery, superstition, symbolism, and the supernatural.
Gothic is the portrait of the power of darkness of doom. Gothic fiction attacks the institutions which might inhibit the freedom of the individual. Corruption, greediness, lust is always projected in aristocrats or priests. And all the symbols of authority, secular or ecclesiastic, are in ruins: monasteries, churches, abbeys, castles, mansions, towers, ramparts. The Gothic hero is a rebel and he challenges the rules and attacks institutions. He is, therefore, the enemy of heaven. Through the Gothic modes, the obsessive concerns of American life could find expression.