I think the reason I like the Batman mythos more than nearly any other superhero is because it is, for me, the most believable saga.* What I find most compelling about Batman is how the whole story is an ornate, shifting constellation of plausible human contradictions and tensions. Batman, ideally, I say, tells the tale of people with powers they are not necessarily born with or stung (or bitten) by, but enter by stages. Batman is full of characters beset by a perpetual madness, or a perpetual hope––a dream of any shade to which they always find themselves waking. This is how our own life is: not a sudden transformation from one page to the next but a steady, complex growth towards some goal or vision, or, perhaps, Dantean descent from them. Batman reflects actual human life, while dramatizing it, as a constellation of slow, organic becoming, or becoming undone. Without these tensions, as a drop of water without surface tension, Batman collapses. The tensions in Superman or Batman are much reduced, or at least, much more one-dimensional. Superman does not struggle with a dark side; Clark Kent goes from being good to being supergood. Peter Parker, likewise, only struggles with his love for Mary Jane, not with his own commitment to justice, mercy, and a balanced, upright life as a "nice young man".
But I think Batman presents much more complex scenarios. Publicly Bruce Wayne is an effete billionaire, but privately he is a man austerely obsessed with avenging his parents as symbols of all innocent victims. His eccentricity is always tinged with a subliminal anger and grief. Batman, the alter ego he creates, is no less contradictory. To the people of Gotham he is seen as both a menace and a hero. Wayne decides to become "the batman" precisely because he thinks the best way to fight crime is with fear, and bats are potent symbols of fearful things above lurking, lunging, and bumping in the night. His "hero", then, is, from the outset, intentionally steeped in menace. He is a knight, yes, but a knight in shady armor. The Joker, in turn, is both a clown and a demon. He somehow makes crime seem like fun, and, by doing so, ironically tries to depict Batman as a thick-headed, humorless, stick in the mud on behalf of a doomed society. Harvey Dent, of course, archly typifies the theme of internal tension in the Batman mythos, insofar as his personality is both that of a lawman and a bouncer, and, then as Two Face, is both perfect pardoner and implacable punisher. The meta-structure of Batman as a world of human tension should, then, be mimicked in each character.
In light of all this, despite all the hype working for Heath Ledger, I believe that Jack Nicholson's Joker in Tim Burton's Batman is vastly superior to Ledger's in The Dark Knight. I know it is not about "comparing" and "hating, but I believe people are getting so carried away with the sheer lethal bizarreness of Ledger's Joker and the cultic status of Ledger as a cinematic martyr, or some mix of both feelings, that they are losing sight of just whom Ledger was portraying. I think Ledger gave a tremendous performance as an arch-villain––but not a tremendous depiction of the Joker. Rather, he portrayed a wildly cunning man bent on shattering the sacred cows of both organized crime and organized society. But watching such a malevolent nutjob is one thing; accepting him as "the Joker" is something else entirely. He was just too unhinged and vicious for me to take him seriously as the Joker. Or, rather, I should say: he was too unhinged for me to take him funnily.
How, then, could Ledger be so good as Batman's cackling nemesis and yet so bad as the Joker? The reason is simple: Ledger's Joker was not funny. He was witty in that "yuck yuck, ya get it" sort of contrived way, and he was "funny" as in creative, but he was not actually, viscerally, believably funny. Even the supposedly "hilarious" scene in which he is in drag as a nurse was much too grotesque and tense to be really funny. Not once in the whole movie theater, except maybe in the early scene where he made the pencil "disappear" did I hear from anyone anything like a giggle, chuckle, or laugh––no one laughed at the Joker for two-and-a-half hours! Jack Nicholson's Joker, by contrast, was simply hilarious. He forced the contradiction the Joker––that of funny brutality, that of the evil we should not laugh at but can't help laughing at––not just upon you as a cinematic formality but onto your own mouth as a spontaneous reaction. You honestly did not know whether to grimace or laugh at the antics Jack's Joker pulled in Burton's Batman (mainly because you usually do both while watching him). The problem is that an unfunny Joker is simply not the Joker, no more than an overly compliant, chivalrous Batman is the Batman.** Ledger's Joker was deranged and "strange" but not once did he make me laugh. He sickened me without ever trying to win me over despite myself, which is exactly what makes the Joker such a compelling villain. He was all seething rage and implausibly deft plotting. Because he was so possessed by his own madness, rather than the witty possessor of it for ill, he was more like one of the hapless inmates of Arkham that the Joker would conscript than the actual Joker. He was so insane and chaotic, in fact, that I couldn't simultaneously believe he was a force of pure chaos and the mastermind of highly coordinated "gag" after "gag" he pulled as the film progressed. Jack Nicholson's Joker could only exist in the world of Batman; Ledger's Joker, by contrast, could be placed in any thriller as either a "clown killer" or even a crude copycat of the Joker for ironic effect.
That, I suppose, is both the glory and the shame of Nolan's Batman movies: they are such good movies that they could actually work without any reference to the specific mythos of Batman. The Dark Knight is a dark, heavy, intelligent, grueling meditation on human goodness and evil––oh, and, by the way, it is quite often about Batman.
* I must make it clear, however, that the absolute top hero in my book is Wolverine. His tale is not only just as gritty and believable for me, but also a source of intense personal support during my adolescence. But anyway.
** This is the problem I had with Bale's Batman, by the way, although I have never seen a sufficiently conflicted Batman onscreen.
Having said all that, let me post as an addendum a script proposal I want to send to director Nolan for the third, possible installment of his Batman movies.
If the Riddler is the villain, I suggest accounting for his compulsion to use riddles by making him slightly autistic. Mr. Nolan had indicated he wants to make his portrayal of Batman more real-world than other versions. Hence, for example, we have a plausible explanation for just where Batman gets his gadgets. Likewise, the plausibility of Nolan's Batman inclines him away from the Penguin as something too hard to "realize".
In light of Nolan's directorial aims, I think making the Riddler autistic would aid the story in two key ways. First, it would make the story more complex by gilding the Riddler's wickedness with a pitiable medical condition. Just as we had to wrestle with a faint urge to pity the (abused? betrayed? abandoned?) Joker in The Dark Knight, while at the same time, loathing what he stood for, so we should have reason both to pity and fear the Riddler.
Second, a mildly autistic Riddler would provide a realistic psychological mechanism his crimes. Since he was a child, he has been baffled by normal social interaction (cf. Baron-Cohen's Mindblindness) and has found a sort of refuge in the dramatic superiority of his memory. He is not so autistic that he can't interact with people or grasp things like envy, status, etc., but he has had to learn them all like a foreign language in order to function well in society (cf. the case of ** in the same book by Baron-Cohen). At the same time, because he has a photographic memory, computer-like computation abilities, and a vast supply of trivia (historical, scientific, mathematical, literary, biographical, etc. facts), he is able to intimidate others by challenging them with obscure, complex riddles. He simply can't help but see the world in complex but socially irrelevant patterns and form arcane associations between anything he perceives. It is from this thesaurus of arcana that the Riddler is able to generate the puzzles he makes; and it is from this awkwardly socialized isolation that he finds the motive to do so.
This would make the portrayal of the Riddler something like a mix of Hoffman's Rainman, Ferrel's Crick, Crowe's Nash, and Carrey's vengeful, slighted Edward Nashton. His mind is constantly working the associative angles and he constantly feels paranoid other people are plotting against him, since, at bottom, he finds normal social interaction threateningly inscrutable. His riddles are his method for expanding his own private, compulsive, fact-laden world to subsume the complex, subtle social world of people he sees as mentally inferior, and as a way of finding his own peace of mind within. He literally lives in the world of his trivia and over time develops a sociopathic urge to make the rest of the world inhabit it too. If the world is hamstrung by riddles only he has the cognitive capacity or patience to crack, then he really is supreme, if nowhere else than in his own mind. It is only because he couples this private megalomania with such dangerous threats (bombs, poison, etc.) that the world must heed his compulsive cruelty. He would be a pitiful force for obscure complexity that hounds him like a swarm of bees just as the Joker is a wounded force for the inner chaos he cannot escape from.