Very few works have been as widely interpreted as this piece. From being nothing more than a simple story about a bug to an in-depth portrayal of his own unhappy family life. While no one except Kafka can say for sure, and he's long dead, we can only guess at what he was trying to say. Perhaps that's why this story appeals to so many, everyone sees what they need to relate to in it.
A strong feeling of alienation runs rampant throughout the entire piece. First, before we even reach his relationship with his family we learn that Gregor is a traveling salesman. Up before light to be herded into an office and when he's not at the office he's literally traveling isolated in hotel rooms. Even when he's home among his family he sits silently at the table cutting pictures and things from magazines. .
Personally, I feel that Kafka wrote this story to deal with his feelings of loneliness. Gregor after he metamorphoses draws further into himself, until finally at the end he commits the final act of separation Death. He immediately pulls away from his parents having almost no contact with them, except for acts of violence on the behalf of his father, for the rest of the story. His sister stays around but finally pulls away from him as well leaving with nothing but the silence of his own mind. After time he can barley stand himself any longer. Trying one last futile attempt at contact only to be shunned back in his room, left alone to die, silent on the floor of his once bedroom come prison. Alone and dead on the floor his family laughs in the next room. When discovered dead the next morning by the house girl he is disposed of in a hidden manner while his family smiles over his death. .
Kafka felt alienated in his life, from his overbearing father to his inability to have a loving relationship. He was horribly alone, so he wrote a story where his character systemically destroyed all relationships in a drastic and severe manner.