If you close your eyes and squint with a certain, measured accuracy, you might notice that the promotional poster for "The Passing" features the silhouettes of the original survivors from the first Left 4 Dead in the background.

If you go one step further and check the image against the movie posters from Left 4 Dead, you might discover it is actually a mirror image of the pose they struck on "Death Toll".

The scene then, is set. This duplication of assets really does adequately describe what Valve have produced with the first downloadable content pack for Left 4 Dead 2. The Passing hints at innovation, delivers it fleetingly, then returns back to form and offers more of the same kind of action you thrashed through in the retail game. Admittedly, this isn't a bad thing, because Left 4 Dead 2 was no slouch in the pants-wetting department, and The Passing is every bit as suspenseful, gore-ridden and downright terrifying as the game that spawned it. It's just a shame it's all over in about half an hour.

The game picks up with Coach, Ellis, Rochelle and Nick next to the stock car they stole at the end of Dead Center. At this point, they're trapped in an urban environment, and tasked with the goal of escaping around (and under) the town in order to meet up with the original survivors, and presumably move on to the Dark Carnival campaign. The original survivors (one is missing - you can google which as I won't ruin the proposed DLC for Left 4 Dead that is set to deal with it) will implore you to circumnavigate the town in search of a generator which must be fuelled up to lower the bridge, and ensure that the stock car can continue to be used as a viable method of transport.

The DLC is presented in three chapters, the first of which is very much an urban run-and-gun (or hack and slash, if you prefer the excellent melee options as I do), followed by a suitably gloomy foray into the sewers, and culminates with the generator challenge at the port. None of these chapters are particularly groundbreaking - indeed, it's fair to say that the entire campaign lacks the personality of Dark Carnival, and the environmental attention to detail found in Swamp Fever. It does feature some genuinely adrenaline-inducing moments however, such as a sprint through the sewers running head-on into the horde (hint: pack a chainsaw) and some close-quarter residential combat where your flashlight will be of particular use.

There are really only a handful of notable new inclusions for the franchise - a M60 machine gun, the new Fallen Survivor infected, the golf club melee weapon, foot lockers, and the new weekly mutation multiplayer mode. Not bad for a DLC pack, though.

The M60 occurs relatively infrequently, and only contains 150 rounds. It can't be refilled either, so once they're gone, you'll lose the weapon as well. It does a phenomenal amount of damage at close range, so the idea time to find it would be shortly before a witch, a tank, or the horde spawns. At all other times you'll have to be careful to avoid using it, and it becomes more of a liability to cart around with you.

The Fallen Survivor spawns with 1000 hit points, and will only attack you until you shoot back, at which point he'll disappear into the scenery as quickly as possible. At least, I'm fairly sure that's what Valve have intended. As the Fallen Survivor drops health packs, molotovs, pipe bombs and pills, the idea is that you'll head off on a mad mission to kill him and end up surrounded by the horde. In reality, he'll come up to you, and you'll floor him before he can run too far at all. Some tweaking appears to be required before the next DLC.

Melee fans will love the golf club, it's particularly suited for those who are used to the reach of the katana, or anyone with a philandering husband. The other minor inclusion are the foot lockers, which occur randomly and dispense infinite numbers of a particular item, such as pipe bombs or pills. Pretty handy if you're backed into a corner, not so useful if you're making steady progress.

The mutation multiplayer inclusion essentially take all the existing modes, weapons and objects and mix them all together to create an entirely new gameplay mode. The first mutation announced by Valve in their blog is "Realism Versus", in which the realism mode is mixed with the versus mode, thereby removing the outline glows and creating much stronger infected. There's also a chainsaw-only mutation planned, along with 18 others over the coming weeks.

For those PC owners with a copy of the original L4D2, the update will be applied when you next launch the game - at no cost. For Xbox 360 owners, you'll have to decide if it's worth the 560MS Points on the marketplace. I'd suggest that if you managed to make it through the entire game the first time around, then you owe it to yourself to purchase The Passing. Sure, it's short, but the mutation mode is set to add a heap of gameplay over the coming months, so get on board sooner rather than later.