Warning: Wikipedia contains spoilers. If you don't want to know about the plot of the film, don't read this entry.
As a film, Unbreakable explores the role that myth has in our civilization, and specifically explores the way that humans use comic books to explore mythic dimensions of the real world. The film works on a second level, for within the film itself comic books are in a real sense man's last link to an ancient way of story-telling.
Not until near the end of the film does the film reveal itself to be a sort of superhero film, with the lead character possessing strengths and abilities far beyond most mortal men. Many have compared this film with The Sixth Sense because it shares the same writer and director, and star actor, has the same type of plot structure, and reveals an unexpected surprise ending.