I still have my original copy of the Killing Joke and the story coupled with Dave Gibbons work makes it a favourite. I do agree with Alan about the story's darkness. I was not a father when I purchased the book but now I am and with a daughter the shooting of Barbara seems very violent now.
I agree with Vordan's comments regarding Oracle, she was a great female character and good female characters have been missing from Batman for sometime especially in Tom King's excessively long and poor run on Batman.