You might have defined The Metamorphosis as realistic fiction, allegory, surrealism, or a combination of genres using some of the following points:
Realistic elements
Gregor’s family members are realistic because they’re ordinary, unremarkable people with understandable shortcomings. Before Gregor’s transformation, his life was unremarkable too—the hectic life of a sales agent who supports his family.
The settings, characters, and events of the story resemble those of everyday reality.
Allegorical elements
Gregor’s transformation into an insect symbolizes the larger themes of the story, such as isolation and persecution.
After the transformation, Gregor’s actions and thoughts carry greater symbolic significance than they would have if he had continued to be human.
Elements of surrealism
Gregor’s transformation is highly implausible.
The story begins with Gregor awakening from a “troubled dream,” and we’re unsure whether the story is a part of some unusual reality or just the continuation of his dream.
