Seems like DC & Warners recent rotten luck with features has now crept over to their animated ones.
They put in this brand new, early extra half hour devoted to Barbara as Batgirl which has nothing to do with the rest of the plot - this is the Joker's story, not hers - just to try & get around the fact she becomes the typical 'Woman In Refrigerator' later. They failed, because it doesn't change what Joker does later. It's like they were trying to apologize for it in advance of something.
"I'm not smart so much as I am not dumb." - Harlan Ellison
The opening 25 minutes were bland, not exactly terrible (except for the sudden batsex scene that came out of nowhere), but they seemed like the prologue to an entirely different story - here they came across as pointless filler. It's unfortunately pretty typical of current writers to stick in this sort of by-the-numbers back story even where it isn't in any way required.
I noticed amongst the various reviews that some female reviewers complained Batgirl doesn't have a strong enough part, entirely missing the point that it wasn't in any way a Batgirl story, it's about Batman and Joker. The prologue didn't help with that.
TKJ isn't at all one of my favorite Alan Moore stories or DC stories, but I think it could have been done better than this. I haven't been impressed with a lot of the DC animated fare since the nDCU came in.