What happens in Vegas stays in Vegas... unless, of course, you're talking about a zombie outbreak. In that case, what happens in Vegas will slowly spread out across the surrounding area, re-animating the dead and resulting in thousands of painful deaths. Each chomped-upon victim will eventually turn into another shambling predator, a staggering corpse with an insatiable hunger for flesh. Sure, the military will eventually show up; when they do they'll eliminate any perceived threat that stands in their way - and that includes any poor sod who's taken a bite. They might stick you in quarantine, but more likely they'll just ventilate you skull with a few bullets, then drive off in a Humvee singing Minnie Riperton's "Lovin' You," in a strangled voice.

This is more or less the tricky position that Chuck Greene finds himself in at the start of Dead Rising: Case Zero. He's managed to escape Vegas, but on the way out his daughter took a bite, courtesy of Chuck's zombified wife. He's now trapped in the quiet little town of Still Creek, which is currently a little less quiet thanks to the presence of the hungry cadavers in the street. They moan, they stagger about in bad clothes, and they're stupid but dangerous - a bit like the audience of The Jeremy Kyle show. To escape Still Creek, Chuck will have to fix up an old motorbike by hunting down five missing parts; he'll also have to source some anti-zombification medicine for his kid, and perhaps rescue a few other survivors. Alternatively, he can just dress up in drag and spend the day chopping zombies in half with a big sword.

If this all sounds a bit familiar, it's because this scenario is almost identical to the one that Chuck finds himself in at the beginning of Dead Rising 2. The setting is different, but the basic gameplay - from the ticking real-time clock and limited saves to the endless toys and sandbox silliness - is practically identical. It's a clever ploy on Capcom's part: create a bonsai replica of the full game, throw in a few cross-over bonuses (XP and cash earned here will carry over to future Dead Rising 2 saves) and then sell it at a low price - a measly 400 MS points.

You might argue that Capcom are effectively charging people for a demo, and that this is a bit cheeky when we're all used to getting such content for free. This is essentially true, but rather than being a cut-down version of a forthcoming release, Case Zero is a custom-built scenario that ties into the plot of the true game; it's essentially a piece of DLC that's been released before the main course, rather thank after it. More importantly, it offers a commendably large bang for your buck.

Perhaps the most impressive thing about Case Zero is the fact that it plays out almost exactly like a miniature version of the Dead Rising experience. It's not a single mission, or truncated slice of something larger: it's a full scenario, complete with side quests, multiple endings, and the endless temptation to mess around with the tools and weapons at your disposal. The core quest will take a couple of hours to beat, but due to the nature of the game it's highly unlikely that you'll get the best ending on your first attempt.

It takes a clear plan and a dedicated approach to rescue all the survivors, nab your daughter's medicine and fix the getaway bike on a single run; even if you're a Dead Rising veteran you're first stab at the game will find you blindly exploring the town. It's not a huge place, but it still takes a while to work out how to get from A to B, and where the best supplies are to be found. Chuck can only carry a limited number of objects at a time, and since your weapons break or expire after a set number of uses, the game forces you to update your arsenal on a regular basis. If you're feeling inventive, you can combine certain items at a workbench to open up a more creative set of death-dealing instruments. Combing a shotgun and a pitchfork, for example, creates a Boomstick - a ridiculous-looking firearm that skewers zombies and then blows them into chunks, netting you a tonne of XP in the process.

While it's really quite commendable that Capcom has managed to create such a concise replica taster of the Dead Rising formula, this faithfulness also means that Case Zero has the same drawbacks as it's full-blooded siblings (I'm speaking in general terms here, since I've yet to play the final code for DR2). The main stumbling block for newcomers will be the game's steep difficulty curve. You can only save your progress at significant points in the story, or when you get Chuck to visit a toilet - and when you do save, there are only three slots to use. This is actually a 200 per cent increase on the single slot that Capcom gave us last time, but while veterans will be appreciative of this fact, everyone else may be a bit mystified at the developers' efforts to make things as hard as possible.

Even in this baby-sized outing, it's surprisingly easy to cock up the central mission thread if you mess around too much - which is rather odd as the game tempts you to do just that at every opportunity. Ten minutes into Case Zero my Chuck was wearing a pink frilly dress and a cowboy hat, and he when he wasn't ramming a hobby horse through a zombie's chest he was vomiting his guts up (drinking booze now makes you sick, in unpleasantly graphic detail). It's this combination of sandbox playfulness and hardcore challenge that makes Dead Rising what it is. The difficulty will be off-putting for some people, but as I've mentioned before, it's worth bearing in mind that the game is never as hard as it is when you first start playing. With time you learn the ley of the land, how to handle the zombies, and which tools work best in a given situation. You'll also level up Chuck, granting him increased health, speed and carrying capacity, as well as a few special moves. And since your save here can be ported over to Dead Rising 2, your work in Case Zero will ultimately make things easier in a few weeks' time - assuming you buy the full release, of course.

Aside from the difficulty, there are a few technical issues that overshadowing the party. Case Zero isn't the prettiest of games, and while it's still quite neat to have so many enemies on screen at once, the effect is less impressive than when Dead Rising first popped up four years ago. There's also a hefty price to be paid for having all these foes, in the shape of some of the longest loading screens we've seen in, well, yonks. With any luck this won't be such a problem in the true sequel, which should offer large sections of casino and shopping mall to explore at any given time, but here in Still Creek you'll soon grow tired of the breaks in the action. It's also quite surprising that your human NPCs still converse with you via on-screen text, rather than proper recorded dialogue, but at least their AI is an improvement on the braindead behaviour were had before - showing enough simulated intelligence to make rescue missions a relatively smooth process.

For all its originality, Dead Rising 2 smacks of old-school design. Perhaps I should be more critical of that, but it's hard to be stern when the game offers such a good time. We'll have to see how the full adventure fares when we get our grubby mitts on final review code, but in the meantime Case Zero is certainly an encouraging step in the right direction. It's unforgiving and distinctly lacking in eye-candy, but it's also funny, original and challenging, with plenty of scope for repeated play. If you like Dead Rising, this should be a no-brainer; if you're new to the franchise this is a great way to dip your toe in the water. Either way, it's a bargain for the asking price.