Excellent analysis. Couldn't agree more.You're not the only one. I think I've seen more people describe the art as a negative than a positive. I am not one of them. It works on a more visceral and expressionistic level than the more literal art of Mazzcchelli. Thats no slag against Mazzucchelli, if I could draw like anyone I'd draw like him. It's just a difference not just in aesthetic but in purpose. As Miller says "What I'm after when I draw my pictures is your guts. I want you to feel something. I don't want you to like me, necessarily, and it's the same with my characters. And what I'm after when draw is evocation, not pretty. I love beauty, I don't care about pretty."
I don't believe Dark Knight Returns would have worked anywhere near as well if it had been drawn by Mazzucchelli. I also don't think it would have worked as well if it was drawn by Neal Adams or Jim Lee or any other slick, detailed artist. It is purely Miller's vision. He doesn't follow a model sheet or a style guide. Some images are drawn quite realistically. Others are drawn in a very abstract way that completely defies reality. It's the same with his lighting. When it suits him Miller will ignore the logic of lighting (light travels in a straight line from a source and whatever it hits projects a shadow) and light things backwards or with multiple conflicting lightsources or will even eschew a lightsource entirely. His top priority is each panel as an image and what is the best possible combination of black and white to make the reader feel what he wants them to feel. Everything else serves that master.
Personally I think Lynn Varley's colors alone make it one of the most gorgeous and creative artpieces in the medium.