I wrote last week that puzzles can be scary, whether they be mechanics-driven puzzles or narrative puzzles. Knock Knock is a game that fails because it approaches an effort to balance tone and mechanics from the wrong direction: It establishes a good, creepy mood, then asks you to puzzle around in it. This diminishes the horror in the game because the puzzle mechanics distance you from the gameplay, asking you to experience the game intellectually rather than emotionally (“Puzzles Aren’t Scary: Intellectualizing Fear in Knock-Knock”, PopMatters, 31 January 2014).
The iOS game Plague Inc. takes the opposite approach and succeeds. It presents you with a puzzle to solve, encouraging you to view the game as analytically and unemotionally as possible and only when you win does it allow you time to sit back and absorb the horrifying implications of what victory really means.