What were the failures of Aristotle?

Aristotle is widely considered on of the great thinkers in the history of western civilization. He wrote about everything from ethics to biology and metaphysics to astronomy. His works have been seminal in terms of how subsequent thinkers have approached topics as diverse as classification of plants, analysis of literature, teaching public speaking, and formal logic. Although we have advanced considerably in many of these fields over the past two millennia, it isn't necessary to characterize elements of his work which have been superseded as "failures"; it might be better to think of them as pioneering efforts. Newton, whose theory of gravitation superseded Aristotle's belief in the natural motions of elements, acknowledges this when he says, "If I have seen further it is only by standing on the shoulders of giants."
In general, Aristotle's works in the sciences are among those most likely to have been proven wrong with advances in technology. His ideas concerning physics, astronomy, and biology are obsolete. In literary theory, his Poetics, although still influential, is limited by its focus on only a limited number of works of one particular culture, and especially by his ignorance of prose fiction. In ethics, his concept of "natural slavery" is one many of us would find repugnant, as we would his assumptions about gender. One could also say that his ethical and political ideas are limited by a viewpoint that accepts human inequality and the power of elites as natural phenomena. He was also, like most Greeks, rather insular, tending to despise other cultures as "barbaric" rather than exploring cultural differences objectively.