I held off watching this until I'd finished the book. As usual, the screen writers adapt to make, what they deem, as a more watchable event. The complete over working of Ahab and his interactions with Ishmael were trite. The extra sightings and presence of Moby Dick ruined the story and failed to evince the true monomaniacal mind of Ahab.
For a character barely heard of in the book and the whale who isn't present until the last few pages of the book, the film ripped the story apart.
Take it as a stand alone film without the book and it's not too bad.
Review of Moby Dick
