Can anyone give me reasons for why Friedrich Nietzsche was considered a good philosopher?

Nietzsche is probably the single most influential continental philosopher in existentialism and postmodernism. His critique of human rationalism and the tradition of western philosophy itself laid the foundations of contemporary continental (European) philosophy.

He is not a more influential or more important philosopher than Plato. Nietzsche was actually critical of Plato, he saw Platonic rationalism as a rejection of the physical world. However, this critique only makes sense in Nietzsche's understanding of society and philosophy -- it's not really a good argument against Plato. Heidegger, a later Continental philosopher who was influenced by Nietzsche, is critical of Plato's ontology. That may be an easier argument to make. There are many articles about Heidegger on Plato if you search Google Scholar.