It was historic because it ended the Napoleonic Wars and ushered in the Pax Britannica. The 19th century belonged to Britain. Until the rise of the United States, it was the grandest empire the world had ever seen.
Also it ended a period (1689-1815) sometimes referred to as the Second Hundred Years War.
It was the last time Britain and France fought. That's pretty astounding when you consider the many centuries of warfare between the two nations. I wonder if the men on the battlefield grasped its historicity. It's not possible and that right there is a lesson about history, man's knowledge and perspective.
For those interested...
I think the 1970 film starring Rod Steiger and Christopher Plummer does a fine job, especially for a historical movie. Usually they slaughter the truth, but this one despite a few minor points accurately portrays the events and certainly captures something of the atmosphere and mood of that watershed moment.