Still, if you're struggling to get past a certain section, it will often be because of a problem within your group. Left 4 Dead 2 is very much a team game, and to get the most out of it you'll need three other friendly gamers - because playing alone with the AI is as dull as a milk-flavoured milkshake. Unfortunately, "friendly gamers" can often seem as rare as rocking-horse poo, so ideally you'll be playing with people you know. In contrast with most online shooters, where conversation essentially equates to being screamed at by a 14 year old kid from Kentucky. headsets are all but essential here. I know that 93 per cent of communication is non-verbal, but in Left 4 Dead the only thing your body can say is "Eat lead, sucka!" or "Oh bollocks, I'm dying." Actually, that's not quite true: the four characters here are far more verbose than the previous game's cast, and they'll frequently come out with excellent snippets of dialogue. Still, my point stands.
Aside from the occasional bouts of being irritatingly aggressive, the only criticism I can make of this sequel is that many of its structural changes are minor. I know there's the whole "If it ain't broke don't fix it," argument, but it's still something to be taken into account - especially if you own the first Left 4 Dead. To be fair to Valve, there are now several alternative game styles to play if you fancy a change from the norm. For a start there's a version of the Versus mode from the first game, wherein one team plays through stages as the Survivors while another quartet plays as Special Infected. There's also a Survival mode where teams attempt to last as long as they can against a never-ending wave of threats. But if you're looking for a hardcore challenge, Realism mode is your best bet. Here you play through a chosen scenario as normal, but without any of the visual aids that help you find pick-ups - or indeed your friends, should you get lost. You foes are also harder to kill, and if a survivor dies then they're gone forever. These changes have a surprisingly large impact on the game, to the extent that teamwork becomes essential at all times. It won't be for everyone, but gamers who like a rough ride will get a real kick out of it.
Finally, but by no means least, we have Scavenger - a competitive team game that turns the fuel-based finale of Dead Center into a four-on-four contest. One team is given a limited amount of time to fill up an engine or vehicle by retrieving gas tanks dotted around the map; the other four players control respawning Specials and attempt to hinder their progress. When time runs out the sides swap over and the game plays out again. The team with the highest score wins the round, and after a set number of rounds an overall winner is declared - matches use a fighting game-style best of 1/3/5 structure.
This may not sound like a particularly big deal, but trust me when I say that Scavenger is one of the best multiplayer experiences of 2009. Obviously a lot of the mechanics from the main game are present and correct, but the pace of the action is faster and more free-flowing. There are fewer standard Infected around and more Specials, and since the latter are now controlled by humans, there's now a need to out-think your opponents. As with Versus Mode, it's incredibly fun to play as the Infected - particularly if you're controlling a Spitter, as his corrosive sputum can set the fuel cans alight. There's a special kind of evil fun that can only be had from ambushing a pair of survivors as they approach the generator, where a well-aimed gob can cause total havoc. Until you've seen a burning man fall over into a pool of acid, you haven't lived.
Aside from being great in its own right, Scavenger shows us that Valve is starting to think about ways to expand the remit of the Left 4 Dead experience. Make no mistake, this is an excellent sequel that does much to build upon the foundations of the first game; however, if there is to be a third entry in the franchise - and I've no doubt that there will be - then Valve will have to go further with its changes. But hey, that's something to deal with in the future. For now, we have Left 4 Dead 2 - a top-quality shooter with oodles of style. And for that, we should be truly grateful.