Imagine a language with a programmable object system. Programmable representation of methods and classes. Programmable evaluation order. Programmable persistence, sharing, and initialization.

http://lispm.dyndns.org/documentation/amop/toc.html

Wherever you see the word "Protocol" in that index, it means there are hooks in place to let you override the defaults.

Common Lisp is so malleable, every programmer is almost forced to become a language architect. You will spend a great deal of your time searching for the most aesthetically pleasing way to do something, instead of the easiest.

The best part is your ability to step into macro expansion one step at a time. You will never be confronted with a pile of machine generated low-level rubbish. Macroexpand-1 each form, repeatedly, and you get to see the onion unfold in slow-mo.