5. Tension
For a game like this to succeed, it needs to push the player's buttons and keep them in a heightened sense of panic as much as possible - in between some well-placed downtime, for the sake of our mental states, of course - and The Last of Us does this like few games out there. The fungus has turned The Infected into contagious, rabid monsters, ranging from the more placid Runners to their final mutation, the blind but immensely vicious Clickers. On top of this, there are other humans who prove far smarter than the Clickers, meaning that you'll have to constantly be changing up your strategy during combat. The Infected are best approached with stealth most of the time - as they use echolocation to hunt you - whereas the humans can be engaged in more confrontational, cover-based combat. However, maintaining the tension even then is the scarcity of the ammo throughout; you'll also need to improvise weapons from time to time, and this along with healing needs to be done in real-time, making mid-battle scrambles for supplies all that more frantic. Few games in recent memory have put me on edge as much as this, and what a feeling it is.