What is the primary disadvantage of the creature's "education"?

Answer: he has no one to talk to.

Frankenstein or the Modern Prometheus is a novel by English author Mary Shelley. The book tells the story of Victor Frankenstein and his Creature, born out of a scientific experiment.

The Creature is intelligent and very interested in human life. While living next to a cottage, the Creature observes the human family that lives there, and based on his observations he learns to talk. He also finds some books and learns how to read. However, despite acquiring this education, he suffers because of his loneliness, and is heartbroken to find out he scares everyone.