What makes Emacs genuinely great? Not that it was built a long time ago and withstood the test of time. Not the fact that it is absolutely free to use, distribute and extend. Not that it doesn't have tons of bugs (it does), or has superb support for every known programming language (it does not).
To understand what makes Emacs so awesome, to learn and master it, one simply needs to embrace the single fundamental truth about it. Emacs based on Lisp. And please don't make a mistake - I am not talking here about a programming language. I am talking about an idea - one of the most magnificent ideas in computer science. Embrace the awesomeness of that idea, the fluidity, and malleability of the structure. Accept it with all its incredible power and some unavoidable flaws - and you will gain superpowers. Which is not necessarily a good thing. Let me explain.
There's a scientific term "umwelt" that biologists use to describe the world as experienced by a particular organism. Every one of us has this "umwelt" - our "subjective view of the world." Our umwelt is limited by our physical and mental capabilities, past experiences, and social circles we grow up and live. e.g., your subjective understanding of Renaissance Art would drastically differ from when you're taken to a museum at the age of three, and when you go there as an adult, or after studying art for fifteen years.
Learning and understanding Lisp expands your umwelt. You will start seeing things differently. It doesn't inevitably make you a better programmer; it might, but doesn't guarantee it, just like suddenly gaining the ability to see things in the infrared spectrum not guaranteed to make your life better.
Finally, once you embrace the idea of Lisp, soon enough, you find out - humans have yet to invent a better Lisp environment than Emacs.
And that's what Emacs is - it is not just an editor, it is not a mere IDE. Most importantly, it is a Lisp environment - living, "breathing", dynamic and malleable. That's what makes it so extensible. And that's what makes it so versatile. And that's why it will never die.