What are the major themes and conflicts in The Metamorphosis by Kafka?

The Metamorphosis by Kafka is the story of a man who wakes up one morning having been transformed into a giant insect. The story works primarily on a metaphorical level. It is not intended as a quasi-realistic science fiction story about an imaginary world in which people turn into insects, but rather a story that uses an imaginary physical transformation to explore the theme of people's inner natures.
There are several conflicts in the story. The first is that of the struggle of the Samsa family against poverty. They are striving to maintain their places in a social hierarchy as members of the middle class despite struggling financially. Gregor especially feels himself trapped in a job he hates. His outward transformation parallels the way he feels his job has deprived him of his freedom and humanity. 
This theme of outward versus inward humanity is seen in the conflicts that erupt between Gregor and his family after his transformation. Gregor wishes to hold on to his humanity, particularly in clinging to art and music, but his family are only concerned with outward appearances rather than inward nature and are repelled by his outward form. Eventually, Gregor's self-sacrifice shows himself to be more fully human, despite his bug form, than his family.