I love this movie, both versions (though I'll be talking about Redux specifically here). It's an amazing artifact, created almost by accident. It also looks like the sort of thing that results from a proper sandbox. There are location-based encounters (the French villa for roleplaying, the ambush for combat), random encounters ("Never get out of the boat!", inspecting the sampan), and even dungeon-style location-based adventures (Kurtz, of course, at the end of the river). It also includes short story arcs (the USO show at the supply depot and later at the MASH, for instance) created by moving NPCs from one location to another. Some scenes are mythic in scope (the Do Long bridge, the end of the river), while others are more prosaic in tone (the USO show, again, and the supply depot in general).
We can find inspiration for our games in many places, sometimes not even the ones that we think of as directly applicable.