The movie is indeed an adaptation of a novel by Yukio Mishima. Just to clarify, the novel is not an obscure work. Mishima is amongst Japan's most famous writers and was nominated for the Nobel Prize for Literature three times. Also, the plot of the original Japanese story does not happen in a remote fishing village; it happens in Yokohama, which is one of Japan's largest cities. Lastly, it does not happen in feudal Japan, a fact that would be very evident had someone read the book.
Now that that's been said, I've watched the movie since I very much enjoyed the novel. While I agree with most comments concerning the movie itself, I actually very much enjoyed the ending. Not only would have supplying an ending would have been taking too much liberty, but also it allows the viewer to imagine what would happen. Furthermore, to challenge another commenter, this sort of ending does work in movies and was a common motif of films during this era. Some other notable movies with endings similar to this include Francis Ford Coppola's "The Conversation" and "Parallax View."
Now that that's been said, I've watched the movie since I very much enjoyed the novel. While I agree with most comments concerning the movie itself, I actually very much enjoyed the ending. Not only would have supplying an ending would have been taking too much liberty, but also it allows the viewer to imagine what would happen. Furthermore, to challenge another commenter, this sort of ending does work in movies and was a common motif of films during this era. Some other notable movies with endings similar to this include Francis Ford Coppola's "The Conversation" and "Parallax View."