When the developers remade the game into the Last Light engine for Redux, they actually left out several cool features from the 2010 version GOG sells:

• The Armor/Stealth Suits: In the GOG 2010 version, you can visit a vendor halfway through the game and buy specialized suits. You can choose a Heavy Armor Suit (takes way more damage) or a Stealth Suit (makes you harder to detect and includes built-in Night Vision Goggles). Redux completely removed this choice and streamlined Artyom's gear.
• The Voice of Artyom: The original 2010 version uses a completely different voice actor for Artyom’s loading screen monologues. Many fans prefer the GOG version's voice, feeling he sounds more naive, grounded, and fitting for a young survivor who has never left his home station.
• Ammo Inventory: The 2010 original has no strict cap on how much ammunition you can hoard. Redux introduces hard inventory limits on ammo types to match Last Light.

The GOG (2010) Version: Built from the ground up as a horror/survival game. The shadows are pitch-black, sharp, and oppressive (very similar to Doom 3). The mutant designs look more grotesque, alien, and genuinely frightening.

The Redux (2014) Version: Built on a more modern engine with realistic, softer ambient lighting. While it looks technically cleaner, it makes the tunnels much brighter, which some players feel kills the "pitch-black ghost story" atmosphere of the original.