I won't claim Lisp is the "most dynamic" (I'm not even sure what that means), but Lisp programmers frequently do things that are difficult-to-impossible in other languages:
- create new control structures
- create new syntax for existing constructs (I think every metaclass I've ever seen has its own defwhatever form)
- extend the runtime (every .emacs is a runtime extension, e.g., what would it take to write calendar-mode for another editor?)
Yegge talks about it some here w.r.t. Emacs, e.g., parse XML by converting it to s-expressions, writing functions for the tags you want to process, and actually running it.
