Why?
I won't give any plot spoilers, but I was amazed by the story itself. Even apart from the big-picture "meaning" of the film, Gibson is just a darn good storyteller about these characters. And the cast of unknown actors were fantastic. There is complete conviction and believability in every character.
Dean Semler did the cinematography -- he did the filming of all three "Mad Max" movies, and was the perfect choice for this film.
Having the dialogue completely in Mayan was genius. Kudos to everyone involved with the costuming and special effects.
Then, as for the big-picture "meaning" of the film, Gibson structured it as a marvelous Rorscharch test. It depicts man's inhumanity to man in such a spectacular way, that the viewer is invited to see parallels with the world today. Yet he also offers the hope for transformation and change through transcendent love.