One of the most impressive features involving They Shall Not Grow Old’s 3D conversion is the fact that the picture depth is used to great effect.
Not only are persons and objects separated from their environments, those same environments are pretty deep in their depiction.
Even in the bookending segments where the footage is purposely displayed in a more 2D fashion (reminiscent of the 3D conversion of Tron Legacy), there’s a depth added by using an old time film frame that adds layers to the film.
Peter Jackson explains as much in the introduction shown with the film, and by time the picture expands and immerses the audience in the action of World War I, the 3D effect brings the film into a living, breathing display of humanity.