Wow, I was blown away
I was already looking forward to seeing this "film" (some people prefer to call it an "animated movie" to separate it from film, as a way to denigrate it for being animated, but this movie truly does deserve the title of "film") and after I got done, I was amazed at how much better it captured the idea of story (an old, worn-out hero suiting back up to fight crime again) WAAAAY better than Dark Knight Rises, both in its tormenting of the main character, so you can actually see the build-up as to why he wants to, not simply "Ohp, a bunch of people are robbing again, time to suit up", here we actually see a character who's trying to spend his time getting rid of his memories so he's not tormented by them anymore, partaking in races to dangerous, life-threatening extents, wandering the streets hoping to be attacked by muggers, THIS is the old-aged Batman that should've been in Rises.
The soundtrack also mixes a lot of retro-style synthesizer music mixed with booming orchestral sounds to mimic the theme of old and new mixed together.
The villains in this, surprisingly, were FAR more realistic in scope and scale than Rises as well, with Two-Face being a primary example (if there's one fault with The Dark Knight, it was killing off Two-Face) of a character driven not because of a one-dimensional "ERADICATE EVERYONE, EVERYONE MUST PAY" mentality, but actually a deeply sympathetic villain who, marred by his terrible past, is unable to accept conversion back into regular society and away from criminal life.
The mutant leader on the other hand acts as a metaphor for the new wave of crime taking over, and in a less literal sense, is also vastly more deep and interesting than Rises take on "new crime" where it's all "oooo, he's robbing a stock echange, ooooo, so scary", here we actually have something to be terrified of in a metaphorical sense, where it can be applied to any era in history, or the US for example, 9/11 (which I noticed they changed the name of the Gotham Twin Towers from the Graphic Novel to the Gotham Life Building) where before we knew what we were dealing with, but then after that happened, we were dealing with "mutants" (terrorists) who had changed the way we thought and acted, made us unsure of our safety, made us plead for someone to rise up and stop them.
All in all, Dark Knight Returns Part 1 may not have been as popular as Dark Knight Rises, but it sure as hell has a longer-lasting appeal to it, with a story, characters, and design that will out-last Rises over time. This movie as of right now holds a spot up along side The Dark Knight in terms of favorite Batman movies and is in my top-20 list of favorite films of all time.