Though the legacy of The Killing Joke is most resonant with Barbara Gordon, they actual story is really about the origin of the Joker and the line between him and Batman. Barbara Gordon is only in a single sequence and what happens to her only happens to motivate the actions of other characters. I don't hold this against the story itself. The world portrayed in The Killing Joke is full of tragedy and nihilism. When reading it again, I was struck by how different it is tonally than all the Batman comics published before or since. Though some horrible things happen in the book, it feels like the book really takes place in its own little world, independent of the rest of DC's output. With all that in mind, its surprising that the story eventually become "official" with the Joker's origin and the injuries to Barbara Gordon being carried over into the other titles.
Compared to his other output from this time, I think The Killing Joke is one of Alan Moore's lesser works. The plot is clumsy in spots and the violence doesn't serve a thematic purpose the way it does in Watchmen or V for Vendetta. The art is very nice and the story says some interesting things about the relationship between superheroes and supervillians, but I think its something of a shame that the story has the legacy that it does. As a stand alone story it works well enough, but it suffers greatly from what was built from it after publication.
Don't get me wrong, I think the portrayal of Barbara Gordon as a superhero who happens to be disabled is a good thing. But the credit for that should go to the writers who had to salvage things when DC editors decided to drag The Killing Joke into continuity. There is probably an interesting story that could be told about a hero becoming disabled and continuing the fight crime, but The Killing Joke isn't it and isn't meant to be.
From Batman: The Killing Joke (Recolored Edition)
By Alan Moore and Brian Bolland