The assumption is widespread that Nietzsche's ethics can be explained as the master morality which he diagnoses in the Essay 1 of On the Genealogy of Morality. The assumption is widespread among those who are semi-informed, and even more disturbingly among those who have some claims to expertise on Nietzsche. As a reaction to Nietzsche, it's not totally inappropriate, the texts do provoke the reader to think of master morality as something better than slave morality. That is somewhat different from a committment to master morality as a form of ethics.
Nietzsche sometime says he is referring to a philosophy of life rather than ethics or morality. I believe it would be going to far to say that there is no ethics, or moral philosophy in Nietzsche. However, it is important toı recognise that Nietzsche is challenging (which is not the same as rejecting) the bases of ethics or morality. What he is doing is to find something like what Hegel calls immediacy, and Kierkegaard calls wonder in a reaction to nature and human nature. Though whether that means we can classify Nietzshe with contemporary Naturalists of a scientistic reductionist orientation is another thing. Nietzsche looks at the wonder, or immediacy of the master's view of the world in the most primitive of moralities, the original master morality. That he explains particularly in relation to Homeric heroes, and in general an approach in which mutual obligations are recognised between masters, but not to those outside the relevant group of masters. From this point of view, the masters define themselves as good, beautiful, truthful and so on. The salves are those who have the opposite of those characteristics.
The slaves are not evil, because they behave according to nature in the master world view, they just behave as they do without evil intention. For Nietzsche, the concept of evil is deeply embedded in ideas of soul, strong personal identity, free will and inner intentions. It is the slaves who have a good/evil dichotomy who assume there is strong personal identity and intentionalism. For the master, there are immediate reactions There is no assumption for strong personal identity and all that might go with that: free will, intentionalism, memory over time. These aspects of master morality are clearly part of what Nietzsche advocates, but it is not what Nietzsche advocates as a whole.
Nietzsche is against a metaphysical theory free will, resting as he sees it on a strong sense of personal identity in which the self is a soul thing rather than a combination of forces as Nietzsche thinks. However, he is not against the ideas of autonomy, sovereignty of the self, or self-creation. These are all given great emphasis. Both art and science are taken as products of the creative self, which creates itself as a it creates a perspective on natural forces in nature or the creation of art. The master is not an artist or scientist. Neither of these would be a complete model for Nietzsche. Nietzsche sees value in the life that is like art, he finds that beauty is a product of the desire for happiness. Happiness comes in life led as self-creating and self-legislating. It is here that Nietzsche sees the origin of value, not in the brutishness and borrishness of the master towards the slave. He does not think that value originates in utilitarian calculations of maximised benefits, or any set of abstract principles or social institutions. Nietzsche refers to the master who forgets offence and only takes revenge where it is immediately possible, but he admires the individual with no need to punish or take revenge at all, much more.