Spoilers ahead: for the puzzle and the movies/games
This page reveals all categories and answers for this puzzle. It also discusses plot details, story endings, and other spoilers for some of the movies/games shown.
easy
Developed by id Software
Doom · Quake · Wolfenstein 3D · Doom Eternal
medium
Set aboard a space station or vessel
Dead Space · System Shock · Alien: Isolation · Prey
hard
The game knows it's being played
Metal Gear Solid · The Stanley Parable · Doki Doki Literature Club · Pony Island
Each game directly addresses the person at the controls, collapsing the boundary between game and player: in Metal Gear Solid, Psycho Mantis reads your PS1 memory card and can only be beaten by physically switching controller ports; in The Stanley Parable, the omniscient narrator watches through the camera and comments on the player's real choices, finally addressing them as a person sitting at a computer; in Doki Doki Literature Club, a character becomes aware she is in a game, deletes rivals from the actual game files, and speaks directly to the player through the OS desktop; Pony Island has a demon communicate through the game's debug console and rewrite its source files in real time to trap you.
tricky
Title contains the word RED
Red Dead Redemption · Command & Conquer: Red Alert · Red Faction · Pokémon Red
Four games from completely different genres and eras (open-world western, real-time strategy, sci-fi FPS, and monster-catching RPG) share a single word in their titles: RED. Red Dead Redemption (Rockstar), Command & Conquer: Red Alert (Westwood), Red Faction (Volition), and Pokémon Red (Game Freak). None of these studios, genres, or decades overlap. The word RED just sits there in all four titles and nobody notices until the connection clicks.