Left 4 Dead was a great game. It had the perfect mix of arcadey action and strategic gameplay to entice shooter fans of every skill level, while also having amazing writing and atmosphere that really sold the survival horror aesthetic. Sure, it wasn’t the first 4-player coop (Yahtzee even griped in his Left 4 Dead 2 review about how commonplace those sorts of games were), but it carved a niche for itself that is so prevalent nowadays that I’d call an entire subsection of Co-op horde shooters “Left 4 Dead clones”.

Excerpt from the VentureBeat article “Earthfall is a new four-player co-op shooter akin to Left 4 Dead

Left 4 Dead famously came into existence when the developers at Turtle Rock studios created a comical mod for Counter-Strike that pitted the players against hordes of knife-wielding bots. It was so fun that they immediately set about creating an entire new game revolving around the concept, a game that eventually became Left 4 Dead. This core concept had been done before, most famously in the Killing Floor mod for Unreal Tournament which also later became its own game. But Left 4 Dead had three elements that defined its gameplay: incapacitating specials, objective-oriented gameplay and health as a resource.

Excerpt from the PC Gamer review of Payday the Heist

Let’s talk about all three. Left 4 Dead had the great idea to add elite zombies that each revolved around a different way of pinning a player, forcing that player’s allies to save them within a few seconds. This elegantly punished anyone who ran off without the support of their team while also ensuring that the zombie hordes were a constant threat even to a full-health team. The second great idea was to revolve the gameplay around objectives and make zombie-killing a obstacle but not the goal in itself. The players were never explicitly trying to kill zombies, they were simply trying to navigate through the hordes (or, during finales, hold off the hordes coming to them) until they could reach the next safehouse or trigger some map event that will allow them to continue to a place of safety. This proved to be great for the storytelling element, and also organically created ‘roles’ for the players to assume by focusing on different parts of the team’s success. One player could focus on completing objectives while another kept the zombies off him, and a third player could wield a sniper rifle and explicitly target Special Infected. And finally, Left 4 Dead defined itself by adding finite opportunities to regain health. All four players start the map with a single medkit and will presumably scavenge a few pills throughout the map, but the tension ratchets up as the team runs out of those and must start rationing their health, keeping mental notes on how much longer there is to go before reaching the next safe house. It gives value to every single scratch of health a zombie can remove from a survivor, and these three design choices are the reason Left 4 Dead versus works so well.

Steam review for Revelations 2012

But plenty of games work well within their own product; it’s far rarer to find a game who’s core mechanics are so solid and unique that other developers can shamelessly parrot them in order to piggyback on the successful gameplay. Left 4 Dead‘s dopplegangers started with the 2011 video game Payday the Heist, the first game from Overkill Software. Payday retained almost everything of Left 4 Dead‘s gameplay but moved the atmosphere from zombie horror to white-collar bank robbing. It’s a testament to Left 4 Dead‘s successful formula that Overill was able to take everything great about Left 4 Dead and it still worked despite the fact that Payday hordes are all firing firearms instead of being restricted to melee only. Payday the Heist would be followed by Payday 2, now the developer’s flagship franchise and a game that had arguably eclipsed the Left 4 Dead franchise in popularity.

Excerpt from a GameSpot article on Horrors of the Gilded Age

But just one copycat does not a genre make. Lion Game Lion, an affiliate to Overkill who made several of the most popular Payday 2 heists, is very soon going to release their first standalone title, Raid: World War II. It’s an extremely similar title to Payday 2 except the players are stealing from Nazis instead of cops. Ulf Anderssen, one of the original developers of Payday the Heist, has left the company to found his own called Ten-Chambers Collective, which is currently working on a self-described “4-player hardcore co-op action horror FPS”. Outside of the Payday 2 sphere of influence, Swedish developer Fatshark came out with Warhammer: Vermindtide in 2015, a game which very clearly modeled its mechanics after Left 4 Dead but set everything in the twilight era of the Warhammer universe pitting the players against hordes of giant rats. Before financial difficulties caused the developers to vaporware the title, Crytek was working on a 4-player monster-hunting title set in the 1800s called Horrors of the Gilded Age. Earthfall, an early-access game that just came out this year, is being called ‘a game to play while we wait for L4D3.’ And the less said about the atrocious free-to-play title Revelations 2012 the better, but there’s no denying that it was the first title to bring Left 4 Dead‘s gameplay to post-apocalyptic Mayan ruins. Not to mention, Overkill themselves have been working for the last 3 years on Overkill’s The Walking Dead, thus completing the circle by taking the Payday 2 formula and adding zombies.

Excerpt from the Wikipedia article for Warhammer: Vermintide.

One of the reasons it’s so rare for a successful game to spawn an entirely new genre is that its “spark” not only needs to work when shoehorned into any number of other conceits, but other developers need to take the opportunity to adapt the core concept and then succeed in doing so. Payday 2, as the most successful copycat in the industry, is arguably more responsible for the birth of the “Left 4 Dead clone” genre by showing just how lucratively it can be done.