When I was younger I played a lot of games on repeat. But among the games I played the most was Left 4 Dead 2.

Now, at the time, we could attribute this to my obsession with zombie media. And while that may be part of the picture, it’s not the whole. I loved Left 4 Dead 2 for the same reason I imagine many couch co-op players did back then, it required teamwork. Actual teamwork.

Nowadays, the game remains a celebrated and largely uncontested experience – yes, people love Killing Floor, but it’s not the same, and I’m not going to talk about Back 4 Blood here. Maybe another time. Part of the reason L4D2 is still so popular is the sheer number of mods there are. It’s practically a sandbox now.

But for me, I prefer the vanilla experience.

And that’s what I’m talking about here. Let’s make that clear. The vanilla experience absolutely hooked me as a younger player and to this day remains one of my favourite games to play with friends.

It’s a run-and-gun sprint for survival, a gauntlet that pits players against a ruthless AI Director and – we’re getting to the good stuff now – a cast of unique enemies.

Why Left 4 Dead 2 is so great.

Well, I kind of gave it away, didn’t I? Special Infected. For me, that’s the ticket. Now, I’m not the first to ramble about the Special Infected, but I do think that the game’s AI Director and level design overshadows them. So, what makes the Special Infected so, well, special?

Again, it comes back to teamwork. Resource sharing is one aspect of this, with players being able to give each other helpful items like pain pills and medical kits. And the team can always rescue players that go down. But communication is the core. Players have to communicate, and they need to stick together.

This is all thanks to the Special Infected.

Each special enemy in the game essentially acts as an ambush that punishes players for not paying attention, straying from the pack, or charging ahead without thinking. They also keep players moving. They prevent that classic moment in a horde shooter: sat in the perfect spot, mowing down countless enemies. No real threat, no real danger.

Perhaps most importantly, players that get caught in some of these ambushes can’t get out alone. They need the others to save them. The Jockey is one such example, a fast enemy that – if not caught quickly – will jump on the backs of players and render them useless. Then there’s the Hunter, an enemy that can be deadly if you’ve strayed too far from your teammates. There’s the Smoker, too, whose horrifying tongue can drag you away from help.

Other Special Infected are more specialised, like the Boomer, whose bile can be a death sentence. And, of course, I’ve got to mention the iconic Tank, a bulldozing giant that immediately becomes the biggest threat as soon as they’re on screen.

They all work together, too. They synergise. It’s a brilliant bit of design that forces players to co-operate because, well, the enemies are.

Why do I love it so much?

I love the Special Infected for three primary reasons. The first being that they keep players on their toes. No environment is ever really safe, with the Special Infected potentially lurking around every corner. It makes the game unpredictable, and the road ahead threatening.

Then there’s the simple fact that the Special Infected make the game more dramatic. They provide bursts of action and panic that prevent the game from becoming a flatline, monotonous experience. And this in turn makes each level more memorable.

The biggest reason, though, is how these special enemies can make everyone feel important. There are countless opportunities to save your friends from death, and – best of all – it’s relatively easy to do. As long as you’re paying attention, you can easily shoot a Jockey off of your struggling teammate. This is a shooter where everyone gets to shine, not just the most skilled.

And that’s really what I think more first-person shooters need to do. I’d love to see more co-operative games that make teamwork so fundamental to the experience. Yes, we’ve got games like Overcooked, but how many shooters make teamwork as important and intuitive as Left 4 Dead 2?