I generally find kafka's works as very surreal. There is nothing unique about this book and that is unique ...you'll find the sufferings of a person who keeps his family before himself still could never achieve their full confidence. The metamorphosis does not only depicts the physical transformation, it has also been used metaphorically ( change in the family from unloving and unstable to a loving and stable one).
It highlights theories lies existentialism and humanism throughout and various dilemmas,that protagonist faces at each moment, related to them.