Guerrilla Games released Killzone: Shadow Fall as a PS4 launch title, and many expected that the Killzone series would take the PS4 by storm as it did with the PlayStation 3. However, not long after the game’s release, the developer said they had closed the Killzone chapter of their lives, and then about a year after that, they surprised everyone at E3 with Horizon: Zero Dawn. How did a studio go from Killzone, a dark and gritty sci-fi war to a brightly colored sci-fi game about survival" It turns out that they canceled an unknown project to do so, and the studio voted to work on Horizon over any other project. Game Director Mathijs de Jonge explained the process in a video interview on Game Informer.

We started out with a smaller team to look into exploring what those concepts would mean if we were to develop them. At some point we took two forward, worked on those prototypes for like, half a year or so. And we did some testing with some external people from Sony that are not in our office, and internally as well, and it was kind of 50/50 at some points. We actually put all the feedback that we got into an Excel sheet. And we had these two graphs: What excites you most and what do you think is the most risky one" The project that [stood] out on both charts was Horizon.

While it’s speculated that this second project was another Killzone title, Guerrilla Games is keeping mum on what this prototype was.
Managing Director Hulst added in that the...