Left 4 Dead has stood the test of time, more or less—and while there hasn't been a peep from the series in years, that's more down to Valve weirdness rather than a sign of a lack of interest from players. Half-Life was galactically successful, and we're all still waiting on a third game. Someday, Gabe, someday.
Part of Left 4 Dead's success was down to how straightforwardly good it was. You rock up, shoot zombies, and spam "pills here!" at every opportunity. There aren't classes or progression trees—and while a lot of those bells and whistles weren't common in the ufa888 genre when it came out, it still made the game more accessible and focused. It's also why people are still playing it.
Classes are something Left 4 Dead ignores in favour of simplicity. According to the game's co-lead, however, things could've gone a very different way. In a recent interview with GameDeveloper, Chet Faliszek remarks: "I dearly love the team from Alien Swarm, but I don’t know how many times where I was told to make [Left 4 Dead] more like Alien Swarm."
For those out of the loop, riches777 Alien Swarm is a top-down, class-based shooter Valve released for free back in 2010. It's a great time, but no-one really plays it anymore—due in part to how under-supported it was by Valve. You can still play it, it's just a 13 year old game that didn't really go anywhere. On the plus side, its code became the basis for a very cool Half-Life RTS mod, Lambda Swarm. So there's that.
"I kept saying, 'no, that is the wrong way to go. This game is more mainstream and accessible.' I didn’t want players to need a specific class or else they couldn’t, like, open a door or have a blocking ability."
That's not to say that Left 4 Dead's formula can't work with a more class-based system. Fatshark's horde shooters Warhammer: Vermintide 2 and Warhammer: Darktide do some great stuff with the model Left 4 Dead established—but they're more complex games as a result. You need a bigger cast of bosses, special enemies, and maps to justify the broader range of abilities.
It's more a case that Left 4 Dead was the first game to really establish its brand of horde shooter mechanics. It's a testament to how dang good it was that these later takes on the genre still use so many of the core design philosophies outlined in Left 4 Dead 1 and 2. In that same vein, when a studio's breaking new ground, they ought to keep things simple.
It's not the first time Faliszek had to put his foot down on something, either. In what he later describes as a "non-event", the former co-lead reveals there was a whole, drawn-out argument about the smoker's tongue. "Germany has a law where you can’t hang people in a video game, [and] the Smoker zombie used to grab people by the neck."
I could've sworn that's what the Smoker does, so I went and checked, and—yep, sure enough, the Smoker never actually chokes you. I guess the implication is that it's compressing the chest like a boa constrictor or something. Faliszek says that's because of his intervention, wanting to smooth over legal compliance with laws. "There was conflict there, we had to smooth it out. And of course, if you g2g1bet ask anybody now, they all think that the Smoker is choking you around the neck. Nobody really cares."