I would recommend 'They Shall Not Grow Old' on the iplayer/tv box. It was on BBC2 the other night. Peter Jackson made it using hundreds of old WWI photographs and testimony from those that were there. A lot of it has been brought to colour and 3D.
Probably the closest you will ever get to knowing what it was like to fight in the great war. He doesn't hold back with some of the more gruesome images either. Very humbling bit of TV.

