Answer:
Insufferable
Step-by-step explanation:
"Insufferable" is the word that most contributes to the gothic tone of the passage. In this excerpt, the author describes insufferable as having no redeeming quality or positive effect at all. He repeats the word several times throughout the passage in order to emphasize this effect. Other words that the author use that contribute to this effect are "gloom," "desolate" and "terrible."