Here we go again. You're almost out of shotgun shells, and you used the last of the group's first aid kits to patch up Ellis - the mechanic who got nabbed by a hunter as you sprinted through that last courtyard. The American football coach is wolfing down a jar of painkillers, while Rochelle the reporter is tensely gripping a bloodied frying pan. Outside the safe house door, hundreds of Infected are waiting: the walking dead, whipped into a fury by some form of mystery virus. The situation demands a clear head, but all you can think is, "How could the same sh*t happen to the same guy twice?"

It's a valid question, because Left 4 Dead 2 looks and feels extremely similar to the game we played and loved last year. There's a slight change of scenery, a fresh cast of survivors and a new selection of melee weapons, but on the whole it seems to be the same old FPS. This isn't such a bad thing, of course - let's not forget that Left 4 Dead was our Number 1 game of 2008. What worked then still works now, but this in of itself begs the question: has this sequel arrived too soon?

Some people certainly seem to think so, if the angry boycott group on Steam is anything to go by. But there's also another camp, one with a voice as loud if not louder, that says Valve deserves to be given a break. These are the guys who gave us Half-Life, Counter Strike and Portal, as well as the super-good-value Orange Box. When it comes to first-person shooting, there are few safer hands.

Personally, I suspect that L4D 2 will be one of those sequels that only reveals its true distinctions over a long period of time. The whole Left 4 Dead formula is reliant upon oodles of balance: these games are designed to played over again and again, and any enormous changes to the setup could easily rock the proverbial boat. My initial impression is that this game feels more like a FIFA or Pro Evo-style update than a fully-fleshed sequel, but I'll certainly reserve my judgement until I've played it for a considerable length of time. Why? Because that will be the only way to fully appreciate the impact of the new features.

Take the new melee weapons, for instance. During my recent hands-on I got a chance to try out the frying pan and the fire axe. They both seemed quite fun: the pan makes a great comedy "bang" as it collides with Infected faces, while the axe covers the screen in gore as it chops through a crowd of enemies. I eagerly rushed to use these weapons as soon as I found them, but in both cases I soon grew bored and reverted to my standard firearms. You drop your melee tools if you take any damage while using them, and since you have to be right next to your enemies to use them, this happens quite a bit. It seemed to me that one was far better off sticking to ranged combat - particularly since you still have infinite ammo for your basic handgun. However, later in the day I watched one of my fellow hacks using a frying pan with great success - thinning out a crowd with his shotgun, then bashing down the stragglers from up close. By carefully switching between the two methods, he reduced his need to reload and saved a fair bit of ammo.

Someone's in need of an extreme makeunder...

The point is, there are probably new strategies here if you're prepared to look for them. Of the new primary weapons, the improved assault rifle stands out as a more accurate cousin to Left 4 Dead's M16. It's now far easier to pull off snipe-y headshots, and as a result there's less temptation to adopt a pray-and-spray attitude. The silenced sub-machine gun, by contrast, feels a bit pointless - but if you could persuade a whole group of survivors to use them, I reckon you might reduce the rate at which you alert the Infected hordes. I remember being similarly bemused by the first game's sniper rifle, and that certainly turned out to have its uses.

In terms of other additions, the Infected's main gain is a new enemy type called The Charger - a muscle-bound giant who acts like a slightly weaker version of The Tank: he'll rush in and knock survivors to the ground with a powerful pounding attack, but he'll also go down quite quickly once you open fire on him. There's also a new version of The Witch that wanders around maps, rather than kneeling on the spot and crying. I've not faced her yet, but I'm sure she's a total pain in the 'Arris.

So, there are new weapons and monsters, but perhaps the most notable feature of Left 4 Dead 2 is the inclusion of levels set during the day. So far we've only played The Parish - a sunny scenario that finds our gang of four attempting to escape from an infested New Orleans. There was a brighter, more colourful look to the action, while the Deep South setting undeniably provided a different flavour to the four stages we've had before. My battle to survive carried me through numerous homes and courtyards, up some precarious-looking scaffolding, and eventually to a long bridge, where the escape-finale took place.

To be honest, this last section proved to be by far the most interesting and exciting thing about the sequel. Whereas all of L4D's finales used some variation on the survivors-under-siege theme, this set piece forced our team to climb over hundreds of abandoned cars - fighting a near-endless stream of Infected as we went. This situation created quite a change from the usual dynamic: due to the fairly tight conditions our enemies rarely came at us in overwhelmingly large numbers, and yet there were so many of the blighters that our ammo was constantly running low. There was a constant need to push forward to reach the next ammo stash, but along the way there were plenty of opportunities to climb up to sniping spots in the upper levels of the bridge. It felt like something of an endurance test, and by the time our group reached the far side we were knackered. Unfortunately, at this point the scenery opened up again and we were swamped with infected. I made a selfish run for the getaway chopper, but was swiftly crushed by an angry tank.

The whole bridge section was brilliant fun, reminding me just how good Left 4 Dead can be. There's no doubting that this is going to be a fine game, and anyone new to the series will love it to bits. What's harder to say at the moment is whether it'll be worth getting if you're still spending time with the original. At the risk of sounding like a stuck record, it'll take some time before we can properly assess this game. Valve has given the game's AI Director a whole bunch of new tricks - including the ability to change the weather - so it'll be even better at mixing up the action as you go along. That sounds pretty exciting, but it's somewhat hard to gauge on the strength of 30 minutes play. And of course there are the other four scenarios that we know nothing about, as well as the tightly-guarded secret new game mode. So, how different is L4D 2 from its predecessor? The truest answer is that we just don't know yet - but it's certainly going to be fun finding out.

Left 4 Dead 2 will be released on PC and Xbox 360 in November.