Games need to have a balancing act of fantastical and believable. If you make something too ridiculous, it loses people who are looking for a believable and deep story. If the game is too straight compared to normal life, people will glaze over and the game will fail to keep players attention. These ends of the spectrum are very important and but neither should overpower the other.
When a game is overly fantastical, you can get games like Bulletstorm. Despite being voiced by great veteran voice actor Steve Bloom, the game failed to capture the audience that it could have. The game went for an arcady and fun approach but the target audience wasn’t looking for an arcady feeling game. The primary game mechanic being a gravity lasso device that can lift enemies in the air and slow them down so that the player could line them up for unique deaths for more points. This was a great idea for a fun game but people we looking for something that held their attention more. Feeling like they were in a new and unique world may have made all the difference.
Naughty dog has never had such an issue. While their earlier works were cartoony and aimed at children, they entered the adult market with Uncharted and have shown that they are masters at crafting a universe that is both unique and believable. Since this time, millions of people have joined Nathan Drake on his adventures around the world. Still, Uncharted was like an Indiana Jones type world, while they turned the world on its head with The Last of Us.
The Last of Us took us to a world of zombie like monsters as we joined Joel in his mission to get Ellie to a lab to see if she holds the cure for the infection. How the world got to this zombie filed state is what's so fantastic about Naughty Dog. They didn't just look at what a world filled with zombies would look like, they imagined how the zombies themselves would be created. They imagined a fungal infection much like the fungus Ophiocordyceps unilateralis, which is able to take over an infected ants behavior and causing it to move to a habitat that is more suitable for fungal growth before killing is host in a location it can reach a new host when it releases is spores.
This complete takeover of the hosts motor functions is presented in the infected in the game as they move from normal human living spaces to more damp and dark areas, areas ideal for fungal growth. These infected are simply called runners because they can see humans and will run after them. Eventually, when the infected human has enough fungal growth, they will move to an area and release spores into the air where any unfortunate souls will be infected if they breathe in the spores.
Ophiocordyceps unilateralis also has additional effects on the host ants body. After moving the ant onto the forest floor, it will find a leaf and will force the ant to clamp onto the stem of the leaf on the underside. It then keeps the ant in this location until it dies. At this point, the fungus begins growing through the soft tissue of the ant and reinforcing it's exoskeleton, making it much more durable before eventually growing a spore pod out of the ants head.
In the game, the zombies appear fairly normal and only act different than normal people but after some time of having the fungus growing, the zombies have the fungus grow out of their face, covering the infected head, effectively blinding them. These infected then stumble around making clicking sounds and looking for prey, the people of this world refer to these infected as Clickers. These clickers not only have the fungal growth out of their head, but also move in a much more stiff and limited way. They can no longer run but will still pursue prey.
Eventually, the infected human will reach a state where they stop all activity and become a spore colony, filling the area with spores to create more runners and clickers.
This modeling of an infection based on a real world fungal infection brings the world filled with zombie like infected into the realm of possibility. It makes the player feel that this is a real and believable world. It makes the player think “what if” instead of just plowing through hordes of zombies like every other game does.