It's ugly. The frame rate is terrible. It routinely stutters. The clipping is appalling. The cars handle like bars of soap. And it's one of the most expensive games on all of Xbox Live. Guess what, though. State Of Decay might just be your favourite game of all time.

In some ways it feels like the realisation of a dream - one that's no doubt been shared by a good chunk of the gaming population. A fully-realised, open-world, zombie survival simulation; one that's expertly blended with RPG systems, interpersonal relationships and resource management. It's hardcore, unique, and - in a rarity for these days - single player.

Not that it gets off to the best start. The action begins midway through a scrap with a group of Zeds, as they're called, with player character Marcus helping another pair of survivors smash in the rotting brains of a handful of windmilling undead. During this opening skirmish, the framerate routinely drops into single figures, the camera sputters as you try to rotate it into position, and the combat appears to have as much subtlety as Joe Pasquale.

After that, State Of Decay bombards you with an overwhelming battering of information, all of which appears to have no bearing on what you're actually doing (ransacking a house and walking along a river) and only serves to baffle you into near submission. If I hadn't been contractually required to continue, there's every chance I'd have turned the thing off.

I'm thankful I didn't. After a couple of hours, State Of Decay actually begins. You and your group of survivors move into a church in the center of the sizeable open world of Trumball Valley, and begin about filling it with resources, food, and other survivors.

You see, as much as State Of Decay is a game about hitting zombies in the face, it's also a kind of management sim. Your home camp has an overall morale which you must work to maintain, by scavenging for ammo, fuel, materials and grub, as well as building medical facilities and sleeping areas for your ever-expanding crew to use.

At first, all this entails are simple recce missions. Still playing as Marcus, you scout out the local houses and search them for gear, bringing back anything you find. The combat is fine - melee heavy and satisfying, with little finesse. Quickly, though, you can start assigning other teammates to run out and pick up the stuff themselves, as long as you've located it first. You'll build relationships with these people as you help them out on missions, and once they become a 'friend', you can actually swap over and take control of them.

Eventually, the idea is to rotate through a crop of leveled-up characters, taking on missions, helping new survivors out, improving your base and generally having as much of a chance as possible against the relentless undead horde. Any danger of monotony is eradicated by State Of Decay's steady turnover of missions. And this is where the magic really starts to happen.

Like Dead Rising, many missions are time-sensitive, so they'll appear on your map, but it's up to you whether or not you take them on. The way the game's structured, too, means that it'll be impossible to cover everything. If you're the anal type who needs to clear every last thing off a quest log - you're out of luck. You'll be dead by dawn.

Every time you head out of camp to take on a narrative mission (there is a story, but most of State Of Decay's best survival tales happen naturally), you'll inevitably be interrupted by something else and embark on a sprawling misadventure of death, destruction and hurried, terrified escapism, and you'll end up back home having completely forgotten why you left in the first place.

There's real consequence to your actions, too. Death is permanent, and while your player character has the ability to take damage and revive him or herself, cohorts can die. Cohorts that may well have been a player character just a few minutes ago - someone you've spent hours with, who you've leveled-up and geared up. One wrong move, and they're gone for good.

It's not just binary life and death you need to worry about either. As morale drops - which it inevitably will do (especially if you turn the game off with your home base in a poor state - State Of Decay keeps going without you) - survivors in your camp start to bicker. If you don't stay on top of things, your whole camp could fall apart, leaving you without the teammates you need to survive.

The whole game's a delicious, threatening balancing act. You become attached to your characters and protective of your base. Play it too safe, and you'll soon run out of supplies. Stretch your resources too thin, and everyone's going to die. It's a shifting, malleable world, and in so many ways, the ultimate zombie game.

It's funny: before State Of Decay, the last title I played was the startling, generation-defining The Last Of Us. Compared side by side, there's no contest - State Of Decay looks like it was drawn in Crayola by a three-year-old compared to Naughty Dog's game. Weirdly, though, State Of Decay is in many ways more impressive . It's certainly more ambitious..

And while I'd hesitate to recommend it above The Last Of Us - which is infinitely more immediate and broad-reaching - there will be a decent-sized section of the gaming community who'll play this game for hours and hours. Also - it may not be pretty, but credit must go to the solid dialogue, decent voice acting and excellent musical score. Undead Labs have concentrated all efforts and budgetary concerns where it matters.

State Of Decay is an amazing videogame, albeit one hiding beneath one of the ugliest, creakiest engines we've seen in some time. It's a complex, inaccessible beast, but one of the most rewarding and compelling open-world games in years. This is The Walking Dead: The Simulator. And it's every bit as good as that sounds.

Version Tested: Xbox 360

Played for 15 hours