Life on the island of Oahu must be pretty good. All there is to do all day is drive aimlessly around the island's plentiful roads and highways, delivering cars, helping invisible hitchhikers, challenging other rich bastards to races and generally admiring the fact that your island houses, per square kilometer, perhaps the largest collection of awesome cars and high-end retailers in the world. I also think there's something fishy going on; what with all the missions that pay upwards of $100,000 just to drive a car 30km without a scratch. I suspect a little car racketeering going on ... either that or it's simply a sign of too many toffee-nosed rich boys who can't be bothered to drive their own vehicles home. At any rate, one can't help but envisage some nefarious underground car dealer, replete with gap-toothed smile and rasping voice, rubbing his hands together every time you ‘deliver' a vehicle and stroll happily away with your delivery fee.

If you caught the slight whiff of sarcasm in my opening paragraph, let it not deter you from playing Test Drive Unlimited (TDU), because let me tell you, it's a damn fine game and perhaps one of the best representations of one that actively works to blur the line between single player and multiplayer. Put simply, as a matter of fact, it's an awesome game, but perhaps not entirely deserving of its own subheading.

The thing that impresses most about TDU is the way in which most of the promises made about a persistent online aspect to the game have been met, and met well. As soon as you start the game, and assuming you have a Gold Live subscription, you're placed on a TDU server and the single player aspect of the game unfolds at the same time as you are connected to other players. TDU is being touted as a "MOOR”, that is, a massively open online racer. If this sounds awesome to you, it is. And it's entirely possible to see online shenanigans, like players busting donuts and burnouts, as well as the odd profanity as you run up their rear end (ostensibly as an accident), just by driving around the place. Other players show up on-screen as their gamer tag, with a distance to them underneath this, and you can see their position on the map, as well as filter for your friends.

The only unfortunate side to this is that most of the time TDU feels more like an episode of Quantum Leap, as you'll be flogging along with a friend only to see him disappear from your server, with no way of meeting up again until you work out the fiddly left-dpad-right-on-the-dpad lock system for other drivers. However, even if these dimensional rifts stymie meets for you, you'll soon forget it as some other racer burns rubber in your general direction, flashes his/her headlights at you and thus challenges you to an instant race. It really is that quick and easy to get racing with other players – once the checkpoints are set, and this is done totally free-form within the island's borders, you're off and racing!

Scattered throughout the island, which is totally open to your exploration from the beginning of the game, are all the game's missions, located by markers both in the game world and on the map. In a travel method much like Oblivion's, you are able to instantly travel to any road, location or mission that you have already driven to on the island. This is extremely handy for when you want to cut that half hour or so it might take for you to get somewhere.

Missions are varied and are divided into several types. Timed hitchhiker missions see you pulling over to help people in need of a ride, with certain time restraints put on you, as well as a particular amount of damage that can be taken before the passenger bails in fright. Delivery missions see you charged with delivering (mostly) hot cars: there's no time limit, but put just one scratch on it and your delivery fee suffers (you get a bonus for a perfect run). There are also many other missions, including speed camera, timed races and even one huge race around the entire island (put aside an hour or so for that one).

The way that missions become available is actually quite ingenious. For perhaps the first noticeable time in a 360 game (not including those lazy games that simply link achievements to level progression), game achievements are actually integrated into your single player experience. As you unlock achievements, such as driving a certain distance or completing races, your status is upgraded (rookie, amateur, pro etc.) and more missions pop up on the map. Indeed, once you get about 20% of the game's missions done, the map starts to look pretty crowded and this means that there's always something to do.

Which is quite a strange statement considering the fact that there isn't actually that much to ‘do' in TDU – by that I mean that, despite the game's insistence on little cut scenes of your customisable character (you can change clothes at various stores), there's no discernable story or overarching mission driving (excuse the pun) you forward. Instead, TDU pretty much throws the entire island and its almost endless amount of missions, trials and long, winding roads at you and says, "Here, go have fun, see you when you're sick of it!” So it's probably just as well, given the sheer volume of missions and the massive size of the island, that the game is so fun.

But on to the good stuff: the cars (and bikes). Manufacturers such as Alfa Romeo, Ferrari, Mercedes Benz and Lamborghini all rub shoulders in TDU and there are plenty of showrooms scattered about the island for your perusing and buying pleasure. But be warned, some of the cars are as like to burn a hole in your pocket as they are in the tarmac. Really, the whole reason to complete missions is to accumulate money so that you can cruise in style and laugh mockingly at noobs who are still stuck with low-level cars. There's also the fact that most races are divided into car classes, so you aren't able to participate in some missions until you buy particular classes of cars. This see-saw of limited mission design via restrictions, coupled with total freedom and the ability to re-do missions for cash, act to make TDU an extremely deep and satisfying experience, even if you do lament the lack of any explicit direction.

Bike handling has received much derision but to be fair motorbikes are perhaps the most thrilling vehicles to drive in the game, and their steering is geared (there I go again) towards weaving in between traffic and burning out of corners more than for realism. Perhaps the worst aspect of TDU's driving model is its physics, which, though generally good when on the open road, can degenerate if you play around a bit. Run into a wall or pole at 300km/h and you'll stop quicker than a thrown tomato – which is confusing because when you collide with other vehicles (the a.i ones) there's a fairly impressive damage model on display. One has to suspect that the car manufacturers did not want their vehicles to be damaged in the game, so just be warned that super walls and telephone poles can make your gaming experience a fair bit less immersive than it should be. I also found most vehicles to feel a little heavy and, for lack of a better word, touchy. But having never driven at speeds of 300km/h, I suppose I'm not in a position to say whether the experience is incredibly accurate or not and a great upside is that you're never forced to spend all your hard earned dosh repairing cars.

Graphically, the game is quite impressive. At times, when driving along winding roads at sunset, the light blooming through the trees, there's almost a surreal beauty and calmness to just driving around and enjoying the scenery. Cars are extremely detailed and lovingly reproduced too, and although I'm not car expert I can appreciate the individual personalities of each car manufacturer just by driving around and car-spotting in TDU. One small aspect that limits the game is the way that the entire game streams off the disc - this can often cause pop-up and slow-down when driving at fast speeds or navigating the map (which itself is updated in real time). There's also a distinct lack of a night cycle.

Perhaps the only other negative thing that can be said of TDU is that at times it feels woefully under populated. Quite simply, there are no people. Only when you pull up to a hitchhiker marker will you see the person (in a short cut scene) but never in the actual game world. I would have liked some GTA-esque pedestrians to liven the island up a little. There's also something unnerving about the way that so many people are driving about the island yet nobody actually seems to go anywhere. You can literally follow cars around for hours – either they're killing time before they need to pick the hubby up from squash or there's simply nothing to do on Oahu except drive around and waste petrol. The inclusion of police also feels a little tacked on. There are several wanted levels that you go through, mainly for ramming into other vehicles, but police chases are nowhere near as involved or thrilling as recent games such as Need for Speed Most Wanted.

However, these things are soon drowned out by all the fun aspects of TDU. Last but certainly not least, there's the sharing of custom challenges. Scattered around Oahu are drive-ins, which house custom challenges from other XBL players. Most have a modest entry fee and a large winning pot – IF you are the best challenger within a certain time limit (usually a matter of days). What's awesome about this feature is that you can upload your own custom races to the server, thus reaping a small amount of cash from other players' entry fees, as well as having the satisfaction of seeing other racers drive your own tracks. Given the hundreds (and I suspect thousands) of individual roads on the island, the chances of copycat challenges are fairly slim.