It's really such a simple syntax change from f(x) to (f x) yet it makes an enormous difference and opens up a whole new world of possibilities. Sure, there are homoiconic languages in which you can write macros that aren't lisps but the expressive power and ease of use suffers. Take for example macros in Julia (itself heavily lisp-inspired), they're possible but ugly and not nearly as seamless as macros in lisp.