I may have to chew this one over some more, but I just saw Django Unchained on Tuesday night, and I have some powerful but mixed emotions about it. So here's my first take:
Historical confusion: Looking at any movie for facts is a chump's game--we go to movies for Truth. I think you're missing the point if you start complaining that Tarantino has a proto-KKK in 1858 or that slave-owners probably didn't stage fights to the death (how uneconomical!), unless you go on to say "what purpose does this serve in the narrative and theme?" I wasn't bothered by any twist Tarantino pulled on history.
That said, the "that's the way it was" argument is pretty terrible and Taratino pulls that out when discussing the use of the word "nigger." It's true that you get used to that word pretty quickly if you study the 19th century, but when you're playing with history, you can't claim history as your reason. However, I think it worked well here for precisely the reason that David Denby seems to object: a lot of people use it and it comes out differently for each of them.
Old timey (1970s) style and references galore: In high school AP English, my teacher was extolling the virtues of Catch-22's chapter 2, which includes lots of allusions to other literature, to which my friend responded, "so, good literature just means referencing other good literature?" I understand that Tarantino was inspired by a certain set of Westerns and exploitation films, but I just felt like I was doing a lot of nodding along: oh, I recognize that style of title; oh, there's a snap zoom; oh, I've seen grainy film in a flashback before. I understand inspiration and homage, but eventually my neck started to hurt. And no bonus points for ramming Franco Nero--the original Django (from 1966's Django)--down our throats.
That said, I think there's something worth looking at in this movie's overuse of close-ups. (Although that's not just a 70s thing; I just watched Silence of the Lambs and so much of the movie is just looking at faces.)
Color as meaning: Quickly: I noticed a certain visual theme in the constant staining of white with red--the snowy training of Django, the blood-dyed cotton at Big Daddy's plantation, the blood-splattered walls of Candieland. "Finally," I thought, "the lily-white South gets the bloody underpinning exposed."
Overall reaction: King Schultz, the dentist-turned-bounty hunter, remains vague to me. At first, he seems hard-nosed and pragmatic--getting a slave driver to explicitly threaten him so that his attack will be classed as self-defense. He's a classic "I'm within the law" sort of shark, paying a man for Django and then leaving him to be murdered by his other slaves; or collecting the bounty on a man who has given up his thieving ways. But he's not entirely without principle: like many German immigrants, he's against slavery if not an outright abolitionist.
So it's natural for him to free Django--but why help him? Schultz comments that, as a German, he has to help a Siegfried-character rescue a Brunhilda-character, but that seems thin. Have they become friends by now? Schultz definitely grooms him as an assistant and partner, but friend? Or is just the injustice of slavery that motivates him?
All of which leads up to the final scene, where Scultz, the pragmatist, is haunted by visions of slavery's violence--perhaps now that he's exposed as a potential victim. OK, but then why choose this moment to take a stand on shaking hands with the slave owner? There's definite parallels between the two men: both eloquent, powerful, assisted by others, dangerous. But it's not really like Schultz has been forced to confront the similarities; or even, that those similarities have to do with the things that make Schultz tick. So why?
The other characters are less muddy to me, but largely because they are simpler: Candie is a jaded man who likes contests, both with slave fights and with pitting himself against the mystery of Django. Steven is a powerful slave who identifies more with white power and privilege--no wonder that he's introduced taking care of the plantation and signing Candie's name. ("Historical inaccuracy!" you protest. Sure, but for a purpose.) And Django's character deepens as he learns more about the world, changing from sullen slave to talkative con-man and killer, but his motivation remains focused on his wife.
People are going to argue for a while whether this is Django's revenge film or Schultz's (and by extension, Tarantino's) white guilt film.