Whether critics find the darkness of The Dark Knight impressive or, like New York's David Edelstein, oppressive, they all agree: The Dark Knight is the darkest, grittiest, most down and dirty movie ever in a genre not exactly known for realism. But what is it that makes The Dark Knight so dark? It's not only the violence (though it's at times shocking). It's not only Heath Ledger's Joker, or our knowledge of Ledger's sad end (though both the performance and the actor's fate add layers of gloom to the movie). It's not even the end, which it's no spoiler to reveal is far from your typical happy ending with hero triumphant.
The Dark Knight's darkness stems from a calculated decision by Christopher Nolan: to push Christian Bale's Batman into the background. To make, in essence, a superhero movie without the superhero. So what does Batman without Batman look like? And where can Nolan go from here?
From the beginning of The Dark Knight, Christian Bale's Bruce Wayne/Batman is only the fifth- or sixth-most-interesting character in his own movie. (The Joker, Harvey Dent, Gordon, Rachel Dawes, and even Alfred the butler are more intriguing onscreen than Batman.) Sure, it's not uncommon for criminals and supporting characters to be flashier than the superhero in a comic-book movie. It is uncommon, though, for the hero to serve — as Batman does in The Dark Knight — as little more than a patsy: just one of Gotham's wind-up toys, serving only to be set in motion by the Joker and sent into yet another trap. Unlike in most superhero movies, Batman isn't two steps ahead of the criminals, or even of us; instead, he's constantly behind, until even the audience can see the plots developing, and Batman's investigations making things worse.
And so throughout The Dark Knight, Batman himself is further and further marginalized, made more and more impotent. Batman can't stop the violence, can't crack the case, and his inability to comprehend the pure malevolent chaos that the Joker represents costs dozens of Gotham residents their lives. In so exhilaratingly illustrating the expression of that pure chaos — and in the dire straits it eventually puts our so-called hero in — The Dark Knight can be read as a philosophical argument against superheroes in a complicated world.
Which suggests there's not much further Nolan's gritty, realistic style of superhero flick can go. After all, you can't get much darker than a superhero movie that all but makes its superhero irrelevant. What's left? An empty Batcave.