Initially, when Gregor realizes he has been transformed, his reaction is one of acceptance. He has always accepted calmly whatever life threw at him, and this is no different. His immediate thoughts are practical, such as how his family will cope with him and what will happen to his job.
As time passes, he gets used to his body, and starts experiencing some happiness. He has now gotten rid of his human responsibilities, and his insect body gives him new pleasures, such as hanging from the ceiling. He is slowly learning to appreciate his new condition.
However, this change in perspective is not absolute. Gregor is incapable of forgetting his responsibilities to his family and his attachments to the human world. He is confused and guilty about his state, but mostly due to how it impacts others. In the end, Gregor cannot gain the peace that his state might have been able to give him had he not felt guilty about his role in the family.