Since the DC animated movies are on borrowed time. Lets talk about the movies the are closest to the source material they are based upon! Now, for the sake of discussion we are not including any live action movies or shows. I would have to say Justice League War is very close to the book. The fact that there are many scenes that look like they are straight from the book is amazing. So tell me your thoughts.
New Frontier immediately comes to mind. Dark Knight Returns as well.
All Star Superman is very close, the only problem is they left out close to half of the story.
Dark Knight Returns, Year One, and Superman Vs the Elite come to mind.
Not a movie, but the New Batman Adventures episode “Mad Love” is a scene-for-scene adaptation of Timm and Dini’s MAD LOVE comic book.
There are some differences like Joker (and then Harley) blaming Harley for the teeth clue being too obvious, and how Harley passed college. Other than that they are basically identical.