Before I read Aristotle (that is, before I read his works, not before I read _about_ him) I didn't know that you could, or were even allowed, to think as many thoughts as he did during his life. And that you could and were allowed to believe in your own conclusions from your own thoughts as much as he did. Even if he pretty much invented the scientific method of observing, measuring and analyzing the world empirically rather than come up with the principles intuitively in your head, his own thoughts are still what's most impressive about him.
Read his book "Ethics" (or another of them, they're so old that you can often find them for free), and then realize that he wrote books at the same level on almost all topics imaginable. With no prior science to build on top of. I can't explain how impressive what he did is in any other way than that, and the history books doesn't do it justice either. You have to experience his thought process yourself.
Today, nobody seems to think as much and as confidently as Aristotle did. Especially in the Western world, people sometimes believe in science and objectivity so much that they don't have any confidence in their own intuition at all. We have such a good system for knowledge that we can relax and not come up with our own knowledge.
Sometimes you need an example of an impressive person, like Aristotle, to realize that you can be one yourself. Because it's almost impossible to come up with that excellence of a mind by yourself. It only seems to be Aristotle who ever did it.