In contrast to its primary competition in the form of Halo and Mass Effect, Killzone was noted for having a far more grounded take on future warfare. The entirety of the story is confined to a single star system rather than spanning the whole galaxy, energy weapons are almost (but not entirely) non-existant, and both major factions - the protagonist Interplanetary Strategic Alliance and the antagonist Helghast - are human. The Helghast's glowing orange goggles, initially a gameplay conceit for visibility on the PS1's limited hardware, gave them a signature recognizable even to those unfamiliar with the Killzone series, as well.
In 2015, Guerilla Games previewed a new game unrelated to previous projects, called Horizon: Zero Dawn, that would wind up being one of the best-selling games on the Playstation 4. The wild success of the Horizon series dealt the effective end to Killzone.
