The first reason is technological: The Last of Us has perhaps the best artificial intelligence I’ve ever seen in a game. The enemies, behave in amazingly realistic ways, forcing the player to think up equally smart strategies in each encounter.
Human enemies are profoundly smart in that they work together to flank Joel and Ellie – they’ll often yell out their positions to each other, followed by instructions on how to get clear sight lines on their prey. Or when they hear the telltale “click” of Joel’s gun running out of ammo, they’ll advance on him or charge.
The zombies, meanwhile, are truly terrifying in their unpredictability. Some can see Joel coming but others, like the deadly “Clickers,” are blind and depend on their hearing. Every encounter inevitably requires the player to think stealth, with an action plan as backup.