This probably makes me a freak, but I absolutely loved The Metamorphasis, and though I can't say for sure that I know what it was about, I do have some ideas.

Gregor's transformation reminded me of the iminent change experienced by returning soldiers from WWI.  However, Kafka not only speaks of PTSD and insomnia, but also depression, anxiety, and social maladjustment.  What I find to be incredible is that the worst wounds Gregor suffers are at the hands of his own family, when his father threw an apple that lodged into his back.  Although Gregor's metamorphasis is itself excruciating, Gregor resentment is directed towards his family, who has no idea how to accomadate him.  Although his sister tries at first to be understanding and supportive, it is she who loses all patience with her brother.  His madness is transferred to his family, and this is what results in Gregor's demise.  This story is a fascinating "case study" about interpersonal relations following the war. Also, as a parallel to The Waste Land, Gregor dies, ruining any chance of procreation from the male of the household.  Instead, his sister must pursue this family responsibility.

I was really very moved by the story because I felt a connection to Gregor's experience.  I lived in Mexico for 19 months following high school, and much of what I saw during that time affected me when I returned to the United States.  Seeing daily poverty, violence, and chaos changed the person who I was, and I became unrecognizable to my family.  Like Gregor, I didn't leave my room for months, and when I did, negative consequences ensued. I may be reading too personally into the text, but it really did resonate with me.