Aristotle was one of the first thinkers to put together a comprehensive system of logic, science, "metaphysics", rhetoric, and other topics. His view of the kosmos has certainly been one of the most, if not the most, influential world-views in the history of Western thought. While I do find that some of his thought is relatively shallow compared to the divine Plato, it is still important to recognize that Aristotle's work has not only intrinsic value, but can elucidate some of the problems of the "Pre-Socratics" and Plato.

The Categories, On Interpretation and The Prior Analytics are the first three works of Aristotle's "Organon" and contain many of the concepts and distinctions that Aristotle uses in other texts. He even refers back to various parts of "The Organon" when discussing "Metaphysics" in order to remind readers/hearers of the ground he has already covered.

This is a Greek text with facing English translation from the Loeb Classical Library.