It you are Japanese or know something about Japanese mythology and/or whaling culture in japan, then this movie will mean a lot more to you than others.
I know most people who watch this movie will come out of the theater ferociously hating Matthew Barney and be turned off of modern art, but for me, this movie was grounded in ancient Japanese traditions. And to have witnessed it, even if it is bastardized from it's Japanese roots, is a fortunate event.
I'll attempt to write the plot as I saw it.
Barney and Bjork were invited onto the whaling vessel as guests. They begin their journey by transforming into sea spirits through several elaborate and beautiful (however long and confusing) ceremonies and rites of passages . This all happens while the whaling crew perform their duties on the symbolic whale. In the end the journey takes a gruesome turn and the transformation is complete.
This is by no means an easy movie to sit through, be forewarned. However, I believe the value is in your furthered exploration into the subject of Japanese culture, ritual and mythology.
Be sure to check out the exhibit at your local museum if it comes to your town. It is absolutely amazing to see.