The ogn material this adaptation was based on, was released on 1988, by Alan Moore & Bryan Bolland. It was one of the most disturbing, nightmarish made in UK stories, that gave an even more psychish tone to Joker as a character and turned (unfortunately) eventually Batgirl into Oracle.
The graphic novel is only 64 pages long, more like a special-sized story, thus DC decided to write more script, in order to be adapted into a full movie. And that is the breaking point.
THE KILLING JOKE SHOULD BE A 30' SPECIAL, NOT THIS ABNORMAL SNOOZEFEST THAT LASTS OVER AN HOUR! They could adapt additionally another short Bat story and release the equivalent of "Hulk VS", in order to fill the disc time. Although we are years now in digital form and 60' is an ill- forgotten excuse for "minimum time limit".
The first half of this raped adaptation is a generic adventure of Batgirl, in which...
MAJOR SPOILERS AHEAD
...she is a young lady that feels useless and loves Batman. Thus, enter Batsex. These 30' theoretically supposed to make us love her character. Personally, it was horrendous and with a major luck of respect to her character. The worst Batgirl story ever. A young naive Batgirl that is useless and eventually bangs Batman as her mentor...
Then, as of a sudden, Killing Joke strikes. The transition is awkward, bad and the tone is out of scale compared to the first half. OK, it is a good adaptation, but it is so uneven to the first half that you are already tired. Although, the frames sometimes have a pace problem.
IN A NUTSHELL, it is a bad prolonged adaptation and you should skip the first 30' for your own mental sake.
Tingnan pa 
