It takes an awful lot for me to spend extended periods of time playing games. I tend to pick at them, putting in a few hours a day over a week while doing other things in between. So, when GTA 4's game-time stat read 35 hours after just three days and my eyes were blood-shot it was obvious that this was not your average video game - not even your average great video game. After more than 40 hours Rockstar's most ambitious game to date was over and left me wondering if I'll ever be able to look at 'normal' video games in the same way again.

Starting GTA 4 for the first time, it was hard to know what to expect. I knew you played as Niko Belic, an ex-military guy from Eastern Europe, that the game is set in Liberty City and that Rockstar had worked on sorting out many of the issues in previous GTAs, but beyond that I came to the game pretty fresh. As to be expected, the opening moments drip with quality, the kind you'd expect to see in the latest $200 million blockbuster movie. In the office the whole gang had gathered to watch the opening moments. "That's so cool" was said more than once in the first five minutes - before the game had even given me the controls - and it's a phrase that became increasingly common - joined by big grins - over the course of the game.

Things start off unexpectedly slowly. Early missions revolve around helping out your cousin Roman, who runs a taxi cab business. It's here that you'll get to grips with the ins and outs of GTA 4, including the new waypoint system for navigation (in-game GPS), your mobile phone (essentially your link to all your contacts in the game), the new combat system and the way missions work. Of course, you'll likely go off the rails, experimenting with the new physics system by ramming innocent pedestrians with your car or inflicting enough damage to cause your car to explode. It's all very next-gen and far too easy to waste hours of your life on.

You'll also come into contact with Liberty City's finest, the LCPD. The wanted system has seen some changes over previous GTAs, making chases all the more entertaining. Do something naughty, like reverse into a patrolling police car, and you'll have a one-star wanted level. The cop will start a pursuit, staying on you as long as he has you in his sights. Get outside the relatively small search zone for a short period of time and the search will be called off, but things can get a lot worse. Once you get up to a three-star wanted level (shoot a cop or go on a blood-thirsty rampage) things aren't so easy, with helicopters giving the cops an eye in the sky. Just hope you never have to see the dreaded level six.

Gun combat has been greatly improved over the previous games

Cars in GTA 4 all handle very differently, as do the bikes. Larger vehicles are pretty sluggish and don't take to power-sliding around corners all that well, while sportier cars have an almost arcade racer feel, ideal for nipping about the busier roads in Liberty City. The motorbikes are the most nimble though, weaving in and out of traffic with relative ease. It's easy to get a little too confident though. In a car a high-speed head-on collision can see Niko fly through the windscreen, but do the same on a bike and you're guaranteed to be eating tarmac, and whatever else your lifeless body careers into as it flies through the air. Helicopters and boats also make an appearance later on in the game, both offering a far more peaceful form of travel.

As deadly as vehicles can be - you can even manually aim a weapon while driving - it's on-foot where you'll do most damage. With a target lock-on and free-aim system the game has most gamers covered, although it's not quite perfect. In confined spaces the camera can get a little lost and the new cover system occasionally locks you to the wrong piece of scenery. Trying to balance free-roaming gameplay and solid shooter controls can't be easy, but Rockstar has done an excellent job. To begin with you'll be limited to your fists and a baseball bat, but soon you'll have access to a pistol, then automatic rifles, sniper rifles, grenades, molotovs and RPGs - lots given to you for certain missions, but also available at the numerous gun stores in the city.

The characters, Roman in particular, are the stars of GTA 4.

As great as these core elements of GTA 4 are, it's the characters that steal the show and make the game truly special. Niko's cousin Roman is without doubt one of the most charismatic and likeable characters ever seen in a video game, and it's Niko's relationship with him - and his love of family in general - that underpins the storyline. You're never too far from the introduction of a new face and for the first time in GTA history Rockstar has absolutely nailed the mix of comedy and drama - helped by some brilliant voice acting and facial animation. Rather than one scene feeling at odds to another, they play off each other wonderfully, immersing you into the story as you grow to like or dislike the characters - sometimes even determining their fate.

As a 40-hour game for most average gamers you might expect the action to let up a little, but if anything there's always too much to do. Aside from the brilliant and increasingly dramatic story missions there's an abundance of side missions: those given out by the key characters which in turn allow you to call in favours; dating, including certain perks; mini-games such as bowling, darts and pool; getting drunk and wandering around the city in an inebriated state; a working GTA 4 internet service with email, purchasable ring-tones, internet dating and news; and more.

The problem is that you just won't want to stray from the core story missions - they're that good. A realistic city in which you can fire weapons and drive vehicles might sound like a recipe for lots of repetition, but that's just not the case. Although you do carry out missions that are similar, the variety is incredible and often unique in how you personally play them out. One moment you might be taking down managers in a strip club and the next you're robbing a Bank and escaping Heat-style - a mission that must go down as one of the greatest in GTA history.

You've got land, air and sea vehicles to steal.

Liberty City is a brilliant game world. We've had other games that have claimed to be set in real worlds, but nothing has come close to this. The map is split into so many different areas and suburbs that it's hard to understand how Rockstar ever managed to get this game out onto store shelves. The level of detail is just staggering. Whereas San Andreas featured numerous relatively empty 'filler' areas, there's nothing but quality in GTA 4. The city is full of people too, getting on with their lives, getting into fights with each other, talking on their phones and generally acting real. Of course, they're not real, and do display some signs of stupidity - most often in their quite ridiculously slow and poor driving - but any casual observers will be blown away by what they see.

Moving from the quieter areas you begin in to the more densely populated areas of the city is a great game moment in itself. Having played for hours in a poor neighbourhood, only to drive down a glitzy road surrounded by neon signs and billboards, with traffic congestion mimicking that seen in New York, is a sight to behold. The sense of moving up in the world isn't laid out on a plate as it is in previous GTA games; in GTA 4 you'll just slowly realise that you're in a better part of town, living in a better apartment, dressing in better clothes and earning money more readily. It's not an instant thing, and works in conjunction with the storyline, with the bigger fishes appearing as your profile is raised.

Production values are through the roof all over GTA 4, with both versions being about the best you'll see on each console (full console comparison including video). The day/night cycle creates some unbelievable lighting and the weather effects set mood in certain scenes that will likely change if you need to replay a mission. Quite randomly during one particularly morbid mission the weather turned for the worse, and the sky was filled with thunder and lightning. Some players are likely to never experience the mission the same way, but for that moment it echoed the mood perfectly. Praise for the visuals could go on forever, covering the sublime explosions and resulting carnage to the way characters react to being shot in different body parts.

It's a little rough in places, but GTA is still a stunning game to look at.

Equally superb is the audio work, which has most definitely raised the bar for video games. The in-game soundtrack is colossal and varied, and voice work for once really is of Hollywood standard. These are 100% believable characters no matter how extroverted they might be. Rockstar could have released the game in hour-long chunks and it would have been rated up there with the likes of The Sopranos as classic slices of cutting drama. The comical radio talk shows and the hilarious TV shows (viewable from your apartment) are also worth of praise - we'd even pay for more shows released via DLC.

GTA 4 most definitely lives up to the hype surrounding it and will certainly go down as a defining game of this console generation, but it's not perfect. Visual blemishes such as pop-up and a sluggish frame rate plagued previous GTAs, and while nowhere near as bad in GTA 4 these problems are still present. The game puts a visually pleasing blur on distant objects, so your view of the city is still incredible, but as you speed along certain things do pop into view. During the most intense moments the frame rate also takes a dive, but these two complaints aren't enough to prevent GTA 4 from being one of the most technically impressive games ever released.

A problem of more concern is the lack of mid-mission checkpoints. How much this bothers you will be a personal thing, but no matter how long a mission might be, failure at any point will result in you having to start from the beginning. Considering many missions require a lengthy cross-city drive before the action starts, doing this numerous times can be frustrating. You can often take a taxi or one of Roman's cars to your destination, saving some time, but it's a shame Rockstar didn't provide a solution for what could have been a non-issue.

We doubt any game released this year will better GTA 4

Slight problems aside, no-one old enough to play GTA 4 should pass it up. It's certainly a mature experience - in tone, violence and language - but that actually makes it even more unique. For all the controversy that Rockstar generates, GTA 4 has moved video games on to a point that most developers just won't be able to compete with. We all knew GTA 4 would be a great game and sell millions of copies, but I didn't expect it to shame pretty much every other game I've played this generation.

This review is based entirely on the single-player campaign. Head over to our GTA 4 multiplayer feature for our thoughts on the game modes that will keep you playing for months to come.

You can buy GTA 4 for Xbox 360 and PlayStation 3 at GAME.co.uk.