| In 2013, nuclear war had devastated the Earth, wiping out billions of lives. Among the affected nations is Russia, including the now-desolate wasteland of Moscow. A handful of survivors manage to hide in the Metro system, salvaging spare parts and growing mushrooms for food. Animals such as rats, bears, and others are mutated into horrific monsters, while the air in many areas that humans breathe becomes heavily irradiated and impossible to survive in without a gas mask. While there is a constant state of war between the Communists and the Nazis both trying to promote their radical ideologies, bandits are stealing, killing and looting in the metro tunnels, even keeping hostages to gain bullets, which are used as currency.
Twenty years later, in 2033, the northern station of VDNKh, now called Exhibition, falls under attack by a group of mysterious creatures referred to as the Dark Ones. Artyom (Russian: Артём), a 24-year-old male survivor born before the bombs fell and the adopted son of the station commander, is persuaded to leave his home there and seek help from the rest of the Metro by Hunter, an elite soldier of the Spartan Order. Hunter gives Artyom his dog tags and tells him to present them to his superiors in Polis, the "capital" of the Metro, before disappearing while tracking the Dark Ones.
Players encounter human and mutant enemies, who can be killed with a variety of firearms; alternatively, players can employ stealth to evade or silently kill enemies. Ammunition and other necessary items must be either scavenged from the bodies of dead enemies, or purchased from vendors. Some areas of the metro tunnels, in addition to the Earth's surface, are covered in fallout radiation, and the player must wear a gas mask to explore these areas. If the gas mask is worn while in combat, it may be damaged, and the player must quickly find a replacement before they die.
Redux introduced several changes:
- The level "Outpost" now takes place at night, and the sun slowly sets during the level "Dead City".
- several levels were combined into very long single levels with no loading screens in between them.
- Added safes and keys to be found.
- Added wipe feature for water/blood on the gas mask.
- More realistic weapon handling.
- Improved character facial models.
- More dynamic lighting with a greater focus on contrast.
- Slight texture and geometry changes.
- Particle effects reduced.
- New graphics for the load screens to match Last Light's aesthetic.
- Improved UI and tweaks to the AI.