Going Beyond the "Bad Guy"
I remember wondering as a kid why the bad guys were bad. What was wrong with them anyway? I remember my dad joking with me while watching "Batman the Animated Series" that all the villains must be the happiest people on earth because they were always laughing.
"The Dark Knight Returns" takes inexplicably mad villains, and gives them relatable personalities with real world problems and reasoning. Arkham Asylum no longer feels like a prison for every goofy freak in a mask, but an actual hospital with patients suffering serious mental health issues.
Harvey Dent (two face) is in a constant state of post dramatic stress from his horrible scarring, and suffers from associative identity disorder as a result. Eventually, even after successful reconstructive surgery, his mind is still scarred from the ordeal... showing that mental scars can last far after physical, and that when we entertain our darker inclinations in times of self loathing, coming back is rarely easy.
If comics historian Les Daniels thought making Robin a girl was a choice based out of homophobia, he obviously wasn't reading the same comic book I was. I have one word to describe the stories addressing of homosexuality: Joker.
The animated feature tamed this down a bit, but the infatuation the Joker has for Batman exceeds that of villain for hero, and the story boldly and unabashedly translates this. The story shows that Joker's sexuality is somewhat seemingly heterosexual, naming Bruno (a rather masculine woman but a woman I swear) as his "squeeze"... still the Joker is obsessed with Batman, to the point that Batman is his only reason for living, and to the point of a romantic love that transcends carnal eroticism. From the murmurings under his breath of terms of endearment, to the ultimate location of their final showdown... the Joker is a psyche that remains complex and fascinating... delving deep into the similarities that exist between polar opposites... and the overwhelmingly strong feelings that can manifest when faced with a person that truly challenges every belief you have.
Mediums like "Batman the Animated Series" explored complexities within the psychology of criminals to an extent, actually quite impressively so for a format that was designed for children. Likewise "The Dark Knight Returns" digs that much deeper, with a rawness that would have been very inappropriate for a children's cartoon, but is a real gift for those that grew up watching Batman, and are still fans in their adulthood.