Nietzsche is culturally important, but philosophically dubious in the extreme. Some of our current cultural woes can be ascribed to the influence of his ideas. Suppose we take a look at Will to Power #534:
Das Kriterium der Wahrheit liegt in der Steigerung des Machtgefühls.
The criterion of truth resides in the heightening of the feeling of power.
A criterion of X is (i) a property or feature that all and only Xs possess which (ii) allows us to identify, detect, pick out, Xs. 'Criterion' is a term of epistemology. So one could read Nietzsche as saying that the test whereby we know that a belief is true is that it increases or enhances the feeling of power of the person who holds the belief. To employ some politically correct jargon that arguably can be traced back to Nietzsche, if a belief is 'empowering,' then it is true; and if a belief is true, then it is 'empowering.'
A second way to read the Nietzschean dictum is to take it not as offering a criterion (in the epistemological sense) of truth, but as stating what the nature of truth is. Accordingly, truth just is the property of increasing the feeling of power: to say that a belief (statement, representation, etc.) is true is just to say that it increases the feeling of power in the one who holds the belief.
Now suppose we ask a simple question. Is it true that the criterion of truth is the heightening of the feeling of power? If it is, then every truth empowers, and every belief that empowers is true. But surely not every truth empowers. You find out that you have some medical condition, hypertension, say. The truth that you have hypertension does not increase your sense of power; if anything it diminishes it. Or the report comes in that you have pancreatic cancer and will be dead in six months. I should think such news would have a depressing effect on one's vitality. And yet it is true. So some truths do not enhance the feeling of power. Nor do they enhance one's power if you care to distinguish power from the feeling of power.
On the other hand, there are empowering beliefs that are not true. Hitler's belief in his invincibility was surely empowering, but it was false as events showed. Believing that he was invincible, he undertook to do what Napoleon failed to do, subjugate the Russians. Like Napoleon, he failed, and it was all down hill from there.
One can multiply such counterexamples ad libitum. Of course, in constructing such counterexamples, I am relying on the ordinary notion of truth, as old as Aristotle, that truth implies correspondence with reality, correspondence with the way things are independently of our beliefs, desires, and feelings.
Do I beg the question against Nietzsche by recurring to the old understanding of truth? If I do, then so does Nietzsche. For what is he doing with his dictum if not telling us how it is with truth? Is he not purporting to tell us the truth (in the old sense) about truth?
What Nietzsche wants to say is that there is no truth 'in itself'; there are only various interpretations from the varying perspectives of power-hungry individuals, interpretations that serve to enhance the power of these individuals. At bottom, the world is a vast constellation of ever-changing power-centers vying with each other for dominance, and what a particular power-center calls 'true' are merely those interpretations that enhance and preserve its power.
But if that is the way it is, then there is an absolute truth after all. Nietzsche never extricates himself from this contradiction. And where he fails, his followers do not succeed.