It would be impossible to speak about The Killing Joke adaptation without addressing the controversy surrounding a subplot which was added to increase its running time, a detective plot focusing on the strained relationship between Batman/Bruce Wayne and Batgirl/Barbara Gordon. The target of this first half, a forgettable villain who has a grotesque infatuation with Batgirl, commits several unspeakable crimes to overthrow his uncle's operations and goad her into reckless decisions. Batman's role as a surrogate protector to Batgirl is threatened when she not only feels trapped from this (unknowing of what she is going to encounter with this villain), but the two end up having sex on a rooftop and are both are forced to uncomfortably move past it.
On top of the forgettable villain, none of this works. Bruce as a parental figure (which, to the movie's credit, isn't how he's portrayed) and a much older veteran of these superhero duties would never have worked because of the tragic backstory regarding his parents, but he has always attempted to protect Barbara (and all incarnations of Robin, who doesn't appear in this film) from the same mistakes that he's made in the past. Barbara essentially becomes his pupil in this regard, especially in learning how to protect Gotham and become Batgirl. Apart from a romantic subplot Barbara is forced into due to not having a steady relationship from her double life, both characters are unexpectedly thrown into this situation with no substantial buildup or reasoning that leads them to these decisions. In other words, there's really no reason for these scenes to happen, nor is there any connection of this added material to the actual adaptation of The Killing Joke. Introducing new material is fine if the adaptation is too short and a specific running time needs to be met, but the approach of this first plot fails to live up to the remainder of the film and is ultimately not executed well enough to justify its existence.
The rest of The Killing Joke, however, is much better once the actual story begins to be told. Albeit with a few added scenes implying the Joker descending further into violent madness, the adaptation is extremely faithful to its source material and goes after the dark spirit of the graphic novel without taking any further unnecessary detours. Its only weakness overall is a flaw that exists for the entire film; the animation style is too choppy and unrealistic, as if the animators were attempting to create unique traits for the film and stopped somewhere during production before they could fully realize those traits. It also feels too modern and unconvincing in representing the 1980's feeling of the graphic novel.
Aside from this, it is great to see the likes of Mark Hamill, Kevin Conroy, and Tara Strong all returning to these iconic roles as though they had never left. Hamill in particular is at his best as the Joker, taking on a seemingly impossible task of playing the villain in the present time as well as the character he could have possibly been in the backstory. He recites lines as the Joker like darker, twisted, and modern Shakespearean prose, yet his other character is milder and insecure, more akin to characters Hamill hasn't explored in years. His approach towards the Joker's past life has traces of his early acting years within it, but with a larger hint of an older and wiser man. It will certainly be interesting to see his portrayal of Luke Skywalker in the next Star Wars film given the acting decisions he chose for The Killing Joke. Conroy and Strong are similarly at their best, Conroy the gruff and seasoned soldier and Strong the brave and daring fighter. Apart from the mundane story they are forced to work with in the first half, both actors bring their roles to life prominently and help remind as to why audiences loved them there in the first place.
Overall, it's the cast of The Killing Joke which makes this film adaptation worth viewing. Their contributions to the story help to make it believable and interesting, even through the worst moments of the movie. The first plot and stylistic choices are poor and the animation is not very good, but the dark tone is Batman at its core and a reminder of the series' greatness. The controversial scenes are few at best and distracting, but can be easily overlooked by diehard DC Comics fans who are looking for a great adaptation of an iconic graphic novel. In those respects, The Killing Joke is worth the watch - just skip the first half.