It was a book before it was a movie, but the book was an adaptation of the movie's script.
My main concern is the length. Three hours seems a tad long for such a thin story. I don't like Jack Black either, but I suppose I can overlook it.
According to the web, the novel came out in '32. The movie was released in '33. I recall it being a rather epic novel in the spirit of Edgar Rice Burroughs. Denham in the novel alternates between an Indiana Jones type hero and a Captain Ahab type figure (in his obsession to capture Kong.)
Even if it was a novelization of the script, it was well done.
Yeah, three hours is long. Perhaps better to release a tightly edited version for the big screen, and save the extras for the Special Edition DVD.