What if they took the basic idea of horde mode and added plot, colorful characters, innovative AI designed to make each playthrough feel dynamic and unique, and objectives beyond just surviving so that it felt like you’d gone through an epic (extremely gruesome) journey by the time you finally reached the extraction point? The result is one of the best horror games of the 21st century. environment) experiences in Halo 3: ODST, Gears of War 2, and Call of Duty: World at War manifested themselves as more straightforward horde modes where teams of four or five would hold out as long as they could on maps riddled with zombies, aliens, or monsters, developer Valve South (later re-established as Turtle Rock Studios) took things one step further. In the late 2000s, cooperative multiplayer games that pit you and your friends against waves of AI-controlled enemies were all the rage, and Valve’s Left 4 Dead was the king of this subgenre.