I think they're asking what makes CL noteworthy among all the other PLs such that it keeps getting brought up, even though it's not new and shiny or widely popular these days. Same sort of question you'd get about Smalltalk or Haskell.
Lisp evangelists always talk about a moment of profound clarity where the beauty and utility of Lisp just clicks in their brain somehow. I've done a little functional programming here and there so I know what it is, but I just can't fathom why Lisp is so beloved. I can't help but wonder if I knew Lisp (or some other functional language) intimately if I would approach problem solving completely differently.
Objectively, I felt the "power" when I learned macros. You can create any programming construct you like which will be executed at compile time / load time, and usable at runtime.
You will see the magic when you actually try it. No other language family that I know of (except forth or prolog maybe) can do this. Lisp still has the best macro system of all.
