My favourite moment in Left 4 Dead? I'm playing Versus mode, and we've reached the apex of the Blood Harvest campaign in a desperate farmhouse siege against overwhelming odds. I'm part of the overwhelming odds, playing the corpulent blob that is the Boomer. I wobble up to a window and look inside, to see Louis firing away desperately at the horde around him. I just watch, smiling, waiting for him to turn in my direction. Only when he does, when he realises that I'm standing there, do I spray him with my zombie-attracting vomit, prompting another wave of infected to crowd in and hammer him to death.
Actually, writing about Blood Harvest reminds me of something that may be even better. I'm playing with a group of survivors who've yet to make the desperate run across the fields to get to the farmhouse, and I'm trying to explain that the trick is to just get a move on. We get there, get organised and start the clock for the rescue to arrive as soon as we bloody can. It will only get worse. They seem to get it. We drop into the grass and scarper. Sheer chaos. I make my way to the farmhouse, and only then do I turn around to realise everyone I'm with has climbed on top of the enormous pile of hay-bales in the distance and are trying to hold them off there. And I'm alone in the house as the waves start to move in...
No - mentioning that reminds me of something else. It's right at the start of a level. We've opened the door to find a med-kit in the room down the corridor. Now, we've each got a med-kit, so we haven't space to carry the leftover. However, about fifty or so metres on, all hell breaks loose, and I end up covered with vomit, pummelled by a mob and generally taken to pieces. I use my med-kit and weigh the odds... I know there's one back there. It's really near. And since we're playing versus, there's a chance our opposition may not paying attention if I break from the group to run back and get it (the omnipresent AI director would be less sympathetic).
An extra health-pack can be the difference between making it to the next safe room or not. The guys are pressing on but... well, I can make it. I know I can. So I head off through the corridors, on edge, knowing if I spot the infected first, I can take them. I just need to stay calm. Every turn stretches out on the way there. It only gets worse on the way back, as I know they must have noticed I've separated from the pack by now. But all is well until I actually have the group in sight - at which point the infected spring a trap and the party is torn apart even as it's brought back together. By cheery stupid human greed I... well, I was the idiot who got everyone killed in the zombie film. I felt a bit like Judas.
Except, I've misunderstood, because you meant what's my favourite moment in the whole of the game. I thought you meant the last time I played. I'd have to think harder about the other one. Left 4 Dead's a zombie-powered collision between Gauntlet and DOOM, and it generates stories at that kind of rate. In any given mission, someone will mess up or excel in a memorable and amusing manner. Especially the former: in a real way, someone making the unfortunate step of Disturbing The Witch is the late-noughties social faux pas equivalent of Warrior Shot The Food.
Of all the co-operative shooters that have come out recently, Left 4 Dead is the one that goes for it hardest. In fact, it goes for it so hard it kind of goes through co-operative games and out the other side - but I'll get to there eventually. Rather than a traditional linear game, Left 4 Dead's content is divided into four campaigns, set around four traditional zombie-apocalyptic scenarios (hospitals, airports, farms and small towns). You can go through each one in an hour or so on a standard difficulty level, with the time increasing if you up it to expert - especially if you get stuck on the ludicrously violent sieges which close each one.
While you can play them by yourselves with three pretty-efficient bots alongside you (The Chaos Engine is another reference that comes to mind when playing - and you can take that as a suggestion of what you should do now, modders), the real heart is coming in with three friends and talking nonsense over voice-chat with one another. While 4-5 hours of pure-play content (i.e. no significant cut-scenes) is about standard for a modern FPS - whether we like it or not - the real value of the game is brought by what's probably the most innovative part of Left 4 Dead: the AI director.