Thus Spake Zarathustra is certainly Nietzsche's most controversial and probably his most important work. The concepts that "God is Dead" and "Eternal Recurrence" with their attendant ramifications are major features of this work. Highly original and inventive, Thus Spake Zarathustra defies simple categorization. Part literature, part philosophy, it parodies both, in its stylistic resemblance to the New Testament and Pre-Socratic Greek writings.
Through a fictionalized version the character Zarathustra, the legendary founder of Zoroasterianism, Nietzsche propounds a new and different version of moral philosophy. During the course of the story presented in this loosely structured narrative, Nietzsche develops and presents a contrary view of mankind: as lying somewhere between the apes and the ultimate Superman, or Ubermensch. Ranging from unsupported assumptions to rigorous argument - from exposition to dialog to poetry - Thus Spake Zarathustra is a surprising, engaging and thought provoking look at the condition of mankind.
Nietzsche himself considered this to be his most important work. His tragic end, in a state of complete mental breakdown, precluded any possibility that it would be superseded and raised a question of the association between madness and genius.