is the Batman origin that everyone currently knows. It is the origin story that until Frank Miller wrote it, did not exist. And therefore, while the book may not appear ground-breaking currently; at its time of publication it was incredibly fresh. It was the gritty, revenge seeking origin story of Bruce Wayne that audiences wanted.
However, in all honesty Bruce Wayne cannot be called the protagonist in this novel. As I recently read: the protagonist is the character which shows change and development in the novel. And in this novel it is Lieutenant James Gordon who is the protagonist in my eyes. At the beginning of the novel Gordan is a young, almost naive cop, unhardened by the cruelty of Gotham and unprepared for the duties of being one of the few moral men in a city of disrepute. Where on the other hand Batman/Bruce Wayne is the vengeful hero attempting to fight crime, taking bullets and making mistakes all to show (as other reviewers have pointed out) how awesome he is.
Frank Miller's work on Batman in general is always solid and reinforces the idea of the gritty and brooding Dark Knight. However, regardless of who writes a Batman story the character is always greater than the individual writer, much like any other great character of fiction. A strong and powerful character may not be as strong in certain author's hands but nothing prevents them from being altered indescribably (otherwise that is not the same character). One may debate whether the newer versions of Doctor Who, Star Trek, Star Wars and so forth are as legitimate or true versions, but they are the same characters regardless. Batman here may be the gritty dark knight (as in The Dark Knight Returns) but that does not destroy the fact that he can be a more comic or noble caped crusader and still be the same character.