Noteworthy for its format, the book comprises a philosophical work of fiction whose style often lightheartedly imitates that of the New Testament and of the Platonic dialogues, at times resembling pre-Socratic works in tone and in its use of natural phenomena as rhetorical and explanatory devices. It also features frequent references to the Western literary and philosophical traditions, implicitly offering an interpretation of these traditions and of their problems. Nietzsche achieves all of this through the character of Zarathustra (referring to the traditional prophet of Zoroastrianism), who makes speeches on philosophic topics as he moves along a loose plotline marking his development and the reception of his ideas. This characteristic (following the genre of the Bildungsroman) can be seen as an inline commentary on Zarathustra's (and Nietzsche's) philosophy. All this, along with the book's ambiguity and paradoxical nature, has helped its eventual enthusiastic reception by the reading public, but has frustrated academic attempts at analysis (as Nietzsche may have intended). Thus Spoke Zarathustra remained unpopular as a topic for scholars (especially those in the Anglo-American analytic tradition) until the second half of the twentieth century brought widespread interest in Nietzsche and his unconventional style that does not distinguish between philosophy and literature. It offers formulations of eternal recurrence, and Nietzsche for the first time speaks of the Übermensch: themes that would dominate his books from this point onwards.
Harold Bloom has criticized Thus Spoke Zarathustra 's style, calling the book "a gorgeous disaster" and "unreadable".
Other commentators have suggested that Nietzsche's style is intentionally ironic for much of the book. This irony relates to an internal conflict of Nietzsche's: he hated religious leaders but perceived himself as at least somewhat akin to one.