It's interesting to think that not too long ago, say 20 some years, that comic books and the films that followed them were not considered serious literature/art. It was considered the stuff of pulp, B-film material for early film serials, and in some cases, taboo to parents who disapproved of the kids reading it. Today, it is an entirely different story. However, the story of Batman himself hasn't changed much in 70 years. The respect to any comic has grown enormously throughout the late 20th Century/turn of the millennium, but the most memorable stories from such universes still remain as strong in print as they can be on film, if done well. After the great success of Batman Begins, director Christopher Nolan of Memento fame follows his dynamic take on The Caped Crusader's origins and unbreakable mission by pummeling it against a theme of uncompromising madness and criminality. Although Nolan himself has admitted that The Dark Knight is not a comic book film (taking inspiration from realistic looking pictures like Heat and maybe Die Hard With A Vengeance), the film does have its formula rooted in Bob Kane's recognizable designs.
Via Christopher Nolan's interpretation, we truly get to see Gotham City as a living, breathing metropolitan neighborhood and all its inner workings, from the law in town (including the corruptible) to its deeply conniving, troubled lot (including some with redeeming qualities as shown in Eric Roberts' mob boss character). Christian Bale once again dons the cape and cowl, but in this episode his infamous character is INTRODUCED to a character as theatrical as him. This key first meeting has probably happened only once in any previous interpretation of this universe and that is obviously when Bob Kane introduced the Joker (interesting 'sacred' tidbit to consider). Taking notes from Kane's early interpretation of the character and Alan Moore's superb story, The Killing Joke, the Joker sets out to show Gotham City the true sense of hopelessness (remedied only by madness) by robbing it of rules, code, and the great figures that strive to keep this sense of law and order. Not to take away anything from the success of The Dark Knight as this reviewer is referencing the working ingredients that already existed in several successful forms before, to be clear it is Nolan's fascinating strife to motivate every detail of this comic book world in a realistic manner that makes it so enjoyable. Even with Bruce Timm's very intelligently written, animated 1992 Batman: The Animated Series, the Joker's whims are just a given. However in this film, the Joker and many other characters have to philosophically explain their actions. Every character trait, ala Harvey Dent (played by a fascinatingly, vulnerable Aaron Eckhart)/Two-Face's flipping of a coin, is motivated by several realistic variables.
And of course, no review of this film can go on without acknowledging the late, great Heath Ledger's stunning Oscar and Golden Globe winning performance as the Joker. His interpretation of the character creates a frighteningly realistic, yet devilishly quirky personality to what might have been considered at one time, a simple clownish image on the page. It is without a doubt fantastic to see a Batman production translate so straightforwardly in live action: the Joker's sick sense of terrorism, yet his constant tomfoolery into making people think he does not know what he is doing, Batman/Bruce Wayne's sense of selflessness, and Harvey Dent's fall from grace. It is one of the best live action interpretations of it so far. The elements already were there for Nolan and his writer brother, Jonathan, to pick and choose. Their particular assembly works because they see it as serious art. It can be the answer to the Joker's "Why so serious?!..:" the reality can be just imaginative as fantasy.