Nietzsche is notoriously unsystematic, which can make reading him difficult. I would recommend Genealogy of Morals as I think that captures his ethical stance the best. Also, you might want to read Heideggar’s (sp) lectures on him as well as Deleuze’s book Nietzsche and Philosophy. Those two books help to give a general overview of his thought.
His writing is filled with rhetorical flourishes and really is beautiful at times, which led some to count him more a poet than a philosopher. I don’t think his importance as a philosopher can be looked over any longer, and if you want to see his importance I would recommend reading Alasdair MacIntyre’s *After Virtue, *which shows how our modern culture, as far as its morality is concerned, is essentially Nietzchean (and Weberian). MacIntyre considers Nietzsche’s philosophy as the only one, post Enlightenment, that can rival the Aristotelian tradition; although virtue theory is ultimately vindicated against even the great Nietzsche. MacIntyre points out that Nietzsche correctly perceived the “failure of the Enlightenment project’s” attempt at rational justification for morality, and so his negative critique is really something to be marvelled at. Where Nietzsche fails is in his positive arguments (i.e. that morality is radically individualist and the moral man is the one who can successfully invent and enforce his own will on others.)
One other cogent point about Nietzsche is that he has been called an “inverted Platonist” (a term which I think he gave himself), but this is a great way to understand his philosophy (if you are familiar with Plato.) Plato held that there were eternal subsisting Forms that were the exemplars of all that exists in material reality. If you turn that idea inside out, you come to Nietzsche’s philosophy. Nietzsche’s metaphysics (though he would probably cringe at me calling it ‘metaphysics’) is essentially that all is a becoming or happening. All things come about haphazardly by chance. At one point in the Genealogy of Morals he goes so far as to say there is no substance underlying anything in experience, but merely, from moment to moment, a more powerful force overcoming a weaker force in the eternal becoming. (To my mind, this is laughable as experientially, if this were true, it is conceivable that raindrops would turn into birds, or crazy things like this would happen all the time, as there would be no causal link from moment to moment.) Essentially, time is infinite, material forces are finite, and therefore, as time marches on those material forces eternally come together repeating the same process over and over, but all by chance.
Also, those who are stating that Nietzsche was not an atheist, I’d like to know what would lead you to believe that he was not. All I’ve ever read has suggested that he was. I don’t know that he was happy about being an atheist, but as he would say he had the courage of his convictions. If he was not atheist, he most certainly was anti-Christian as his broken friendship with Wagner, as well as his contempt of socialism would show. Furthermore, his contempt for the “priestly caste” (read Jews and Christians) suggests to me that he had a profound disgust with any kind of religiosity, as it allowed the ‘slaves’ to rule the ‘masters.’ The Cross was, for Nietzsche, a constant temtpation for the weak to rule the strong – the idea of a God on a cross was the epitome of slave morality in Nietzsche’s mind.
Anyway, I would be careful reading Nietzsche, and would suggest always having St. Thomas’ texts at hand (if you read latin his whole corpus is online) as he has cogent replies to pretty much anything Nietzsche argued for. Personally, Nietzsche shook my religious convictions to the core, but good ol’ brother Thomas (and certainly grace) kept the foundation strong. After all, as Pope Leo XIII said, Aquinas wrote in such a principled way that he successfully refuted any error that had come before him, or could come after him (cf. Aeterne Patris).