In stark stylistic contrast to almost any work of philosophy you care to name, Thus Spoke Zarathustra dances from the pages with a florid exuberance that can border on the embarrassing. Its scope, as well as its tone, is immense, with Nietzsche's thoughts leaping from mountain top to mountain top, refusing to halt and be restrained by explanations. The final book, comprising four parts written between 1883 and 1885, had a first print run of just 40 copies, such was the author's belief (and probably his desire) that so few would understand it.
It is not a work that follows the analytical tradition of drudging salva veritate pedantry. It is, at its core, a joyous outburst of creation. Until this point in his life, Nietzsche was something of a microcosm of certain consequences of the Enlightenment, with the erosion of religious truths and traditions creating despondency and a fear that values such as "truth" and "good" would lose meaning.
In Zarathustra, ones sees a rejection of this Schopenhauerian world-view and Nietzsche's earlier unsatisfactory attempts to surmount it, in favour of genuine optimism that new values could be fashioned and couched in human terms, not mystical ones.
The central theme of the book for me, the bermensch (the "over-" or "superman"), is key to this revaluation. As with much in the book, too-literal readings of what is often very figurative can lead to gross distortions, as occurred after Nietzsche's death with selectively edited portions of various works. The bermensch is a target, not a eugenics project: a goal potentially forever out of reach as we strive to leave behind so many of the negative encumbrances with which religion, or just blind, unquestioned human tradition, weighs us down.
This was not a particularly popular view a century ago and is not much more so now, despite the current focus on ideological disputes. Certainly, a shallow reading could inculcate the idea that Nietzsche is offering an excuse simply to behave immorally within existing systems of morality. But what Zarathustra strikes us so forcefully with is that settling - for mediocrity, for poor pre-scientific traditions, for the laziness evinced in not advancing ourselves - is appalling. This creates a constant ongoing project of betterment, of struggle and of (in the author's voice) war, that makes the book perennially relevant.
The secondary title of Zarathustra is "A book for everyone and no one". That can be read in so many ways and beautifully encapsulates how openly the text can be interpreted. If one can look past the skeletal plot, manic enthusiasm and casual misogyny, there is much to find in a work of such breadth and depth.
It has affected me very personally, directed me into philosophy and has given me the wry pleasure of attempting to promote a book written by a man who expressed a belief that universal literacy would ruin the value of writing itself.