How do LISP macros differ from others?

I constantly hear LISPers boast of the macro capabilities of LISP. How are they different from, say, the macros one can make in C?

Any LISP macro (regardless of type) just produce more pages of LISP code.
 There is nothing magical and C code is faster than LISP. C macros are used to reduce code density, not to increase complexity of the language.