http://www.apl.jhu.edu/~hall/Lisp-Notes/Macros.html
And here an insightful statement of someone who was sceptical but became a Lisp convert:
http://www.defmacro.org/ramblings/lisp.html
Lisp is so different from all other languages that you have to use it to understand it. Just reading about it is not enough.
Note that there are many variants of Lisp. Older Lisp versions are suitable for experts only. For beginners I would recommend Scheme which is a well defined successor of Lisp. I would recommend Racket (http://racket-lang.org/) as SDK. It is suitable for beginners as well as for professional development.
As I pointed out in a comment at the beginning of the thread, scheme teaches you some habits that don't translate well to other lisps, so to those thinking of picking it up, be mindful of the assumptions of the language, and when you decide to look into other lisps, don't assume they will be the same there as well.
In fact i would actually recommend learning clojure or common lisp before scheme. I consider both of them to be better languages, but i have my own set of assumptions that might not be shared by others :).
I do note the PG quote at the bottom of the page -- "the power of Lisp cannot be traced to any single one of them. It is the combination which makes Lisp programming what it is" -- and I can see that unity being very elegant.
But the real standout item is macros. I suppose it's the only unstealable feature. Or rather, those attempts to steal it, like .net DLR Expression Trees, make really ugly code and are never going to be standard programming techniques.
Anyway -- thought-provoking. Thanks.