Clean Air and Other Humans on the Surface
The big reveal of Exodus’ trailer comes at around the halfway point, when Artyom forces his way out of the Metro tunnels and into the light of day. Previously, wandering onto the surface was a dangerous proposition as it was entirely irradiated and filled with deadly creatures. In Metro Exodus, however, it looks like you’ll be able to journey out to the surface and explore without the limitations of a gas mask.
It’s not quite clear how the outside world is safer at this point, although it could tie into the good ending of Metro: Last Light. In that ending, after finding out the truth about the Dark Ones, Artyom is seen in a field with them, and told things will be better if they go away. At this point, if the Dark Ones have vanished, they could have somehow salvaged something to make the environment livable for human life.
Another thing we see at the tail end of the trailer is that it’s not just Artyom exploring the wilderness of Russia. At the end, he’s saved by a mysterious woman aboard a train, rigged up with barbed wire and other defenses, suggesting that it could be a group or organization traveling aboard it. We’ll certainly find out more about the state of the world as more is revealed about Metro Exodus.
