Killzone was pushed on the narrative that it was a "Halo killer" since its announcement, and it primarily survived because Sony fans couldn't access Halo. Despite being a game with decent atmosphere and visual design, it really didn't need the comparison to be drawn and would likely have been more successful had Sony kept more humble about it. Ultimately CoD surpassed Halo not because it was harped on as a "killer" from day one, but because it was:
1. Multi-platform.
2. Had an established reputation of being a competent series (not by Treyarch at the time).
3. Had a very successful reimagining into the modern era that placed it as a spiritual successor to Battlefield 2.
4. Single-player campaign that was very competent for the time (though in truth Infinity Ward's stories were all good back then. Bar Halo and Half-Life you didn't get much better for an FPS). This offline catering gave it the edge over Battlefield which has persisted to this day.
5. Introduction of a borrowed system that was largely unexplored in its competition at the time, which distinguished it (I,E: perks taken from UT2004 and CS: Source RPG mods). From here they were considered the original creator of "perks" and simply continued to lift everything from their competition into their own game (Bomb Planting mode, Gun Game, sticky grenades, grappling, basically everything from Titanfall, etc.).
All of these things came together to make it the new golden standard for FPS, without the "killer" moniker being attached. Now you see something like Blackout being called a "killer" and that automatically puts pressure on it as being the second-place option intending to overcome the first. Zombies mode was never a "L4D killer"; it was just a borrowed idea that was refined and incorporated into the title to resounding success.
cogconnected.com
