If Adrien Brody is a surprising choice for the "hero" of the story, Jack Black seems born to play Carl Denham. Denham is a man with boundless energy, intense focus, unshakable faith in his own projects, and a slightly disreputable quality - the definition of the archetypal Jack Black role. In spite of this perfect fit, however, some critics found Black's presence to be distracting, anachronistic. I think this is unfair to Black, and to the film.
Having a well-known screen persona is a two-edged sword: casting directors automatically think of you when certain parts are being cast, but then audience members (and critics) keep thinking of your other roles while they watch your newest one. This is a particular risk for outsize comic personalities - Robin Williams being another example; with a strong director and a good script, they can give a good performance, but left to their own devices they tend to fall back on shtick. If Black had kept introducing post-modern touches into
King Kong, approaching the story as if it were
Shrek, he could legitimately be faulted; but Peter Jackson is clearly focused on the story he wants to tell, Jack Black stays in character and in period, and if people look at Carl Denham and see
School of Rock, that's their problem, not the filmmakers'.
It is also worth noting that the character of the con artist and manipulator has not changed much over the last few millennia, so one such portrayal will inevitably bring others to mind, no matter how good the actor. If you read ancient Greek and Roman comedies, you will be amazed how prescient those ancient playwrights were, to have created so many roles for Jack Black.
But in one key respect, Carl Denham is an atypical and more challenging role for Jack Black. Black's character is usually the good guy - irreverent, undisciplined, but on the right side. In
King Kong, we get a much clearer look at the ugly side of this character. We don't see it at first, because the studio executives he is battling are such jerks that he looks great by comparison. (When one executive asks, in his own primitive way, whether Denham's film features female nudity, Denham's reaction is vintage Jack Black.) As the film progresses, however, it becomes more and more obvious how destructive his actions can be. He honestly isn't trying to hurt those around him; he just seems incapable of registering their distress, except when he needs to work around it so it doesn't prevent him from reaching his goal. The darkness, in other words, is an integral part of a more complex portrayal.
One particular scene summarizes Denham's character. (The sequence was cut from the theatrical release for reasons of time, but is included in the Extended Cut on DVD.) Denham is filming as the crew recovers from an attack, when one of them is suddenly swallowed by a huge monster. Lumpy the cook (Andy Serkis' human role in the film), looking on, asks Denham sarcastically, "D'you get that, did you?" Denham's expression is one of horror - but he keeps filming.
Carl Denham is the only one who journeys into Kong's world and is not changed by the experience - precisely as you would expect from this sort of person. Peter Jackson has a very specific reason for making Denham so unsympathetic, but the payoff doesn't come until the last moments of the film.