What's best about Far Cry 2? Is it the astonishingly beautiful African environment, so alive with movement, sound and realistic reaction to your actions that it might just be the best shooter sandbox of all time? Is it that the potential for eye-popping explosions, flying vehicle chassis and spiralling wood splinters awaits around every corner, above every ridge and in every chasm of the huge 50km square open world? Or is it the true freedom the game grants the player, allowing for a plot that has its roots in linear storytelling but provides tantalising off the beaten path branches?

The true answer is that there is no one thing that can be considered best about Far Cry 2. Its brilliance lies in the fact that it is more than the sum of its already impressive parts. Essentially the game is a playground that caters for whatever mood players find themselves in. Want to storm into an enemy encampment in broad daylight John Rambo style, perhaps running a few unfortunate soldiers down with a MG-mounted Jeep before letting loose with your grenade launcher? Go ahead. Prefer to fast-forward the incredible day/night cycle to midnight by taking a nap in one of the Safe Houses and sneak in under the cover of darkness before slicing and dicing from behind with your machete? Be the game's guest.

Ubisoft Montreal isn't, of course, the first developer to do open world shooting. Indeed last year's graphical tour de force Crysis is still fresh in our memories - as is the follow-up Crysis Warhead. But it is so well executed, so technically proficient that we can't help but feel it at least matches Crytek's shooter, and in some areas even surpasses it.

The game's first hour, however, might convince you otherwise, and it almost did for us. After choosing from a selection of nine refreshingly un-clichéd mercenaries, ranging from a 45-year-old Mauritian to a 38-year-old Algerian (when was the last time you could play a game as anyone not of American, British or Alien descent?), you're thrust into an unnamed African country being torn apart by two warring factions. Your mission: To kill The Jackal, an arms dealer who's fuelling both sides of the conflict with weapons, and making a mint as a result. You immediately run into problems - malaria wraps its diseased mitts around your innards, forcing you to collapse as soon as you arrive in town. You wake, groggily, and find The Jackal standing ominously above you. He knows everything - who you are, why you're here and how defenceless you've become as a result of the malaria. In pity, he hands you a machete and a hand gun, and lets you live. This is where Far Cry 2 kicks off.

It's not long before all hell breaks loose, and you're right in the thick of the action.

Outside, all hell breaks loose. The United Front for Liberation and Labour (UFLL) and the Alliance for Popular Resistance (APR) are going at it in the streets. You make a break for it, dodging bullets as you head anywhere as long as it's away from certain death. But there is no escape - either you're shot or you collapse from the malaria. You wake in a slaughter house just outside town. A merc, one that you did not pick to play as at the beginning of the game but is determined by that choice, now reckons you owe him a few favours on account of him saving your ass. From there, it's up to you what jobs you take on, whether it be paid work from the UFLL or APR (diamonds act as currency in Far Cry 2, which can be spent on upgrades), malaria pill jobs from various good Samaritans, weapon vendor jobs that unlock new purchasable gear, buddy jobs that improve your 'history' with the NPC mercs or assassination jobs dished out by a disguised voice heard from communication masts. What they all have in common, however, is combat, and it's here that Far Cry 2 initially frustrates.

We're used to developers holding our hands so tightly during game tutorials, and even beyond, that Far Cry 2 will at first jar with many due to the fact that it's actually pretty tough right from the start. Simply shooting stuff is difficult. Unlike the console versions, the PC version doesn't have a snap to target function when you zoom down the barrel of your gun. This is fine - the PC keyboard and mouse set up allows for a degree of FPS accuracy console controllers simply can't. But this doesn't stop your weapons, especially at the beginning of the game, from being, frankly, crap.

You'll find the recoil offensive, the jamming so regular you'll tear your hair out and the enemies so hard to spot in your splendid surroundings that it won't be long before you grab a mouthful of dirt. The healing system doesn't help. Whenever your health dips you can inject yourself with magic hit point juice. That's fine, but when your health bar is almost depleted healing will instead trigger an animation where you gruesomely pick bullets out of the holes in your skin. The problem is that this animation, which takes about five seconds to complete, is interruptible by enemy fire. Invariably in an encounter during the first few hours you'll find yourself surrounded by enemies you can't see, peppered with bullets that bring you to within an inch of your life and unable to heal because the healing animation keeps getting interrupted. Then you die and reload from the last time you saved.

The combat is at first frustrating, but stick with it, it gets better.

During the first few hours of play Far Cry 2 is almost frustrating as a result of the way its open world gameplay has been designed. It's off-putting and about as pick-up-and-play as a 2D Treasure shooter. You'll want to enjoy the open-world from an almost therapeutic, scenic route perspective, but you can't because driving just a mile down the road will incur the wrath of the game's soldiers as you pass through a check point. And when they force you off the road from repeated bullet fire, reducing your ride to a pathetic mess, you'll sigh. Here we go again, you'll say. Can't an honest merc just get from A to B in this bloody country without having to dodge bullets?

Some will applaud Ubisoft Montreal's approach. Some will criticise it. Whatever your opinion, persevere. Soldier through the difficult opening few hours, keep earning diamonds, keep reducing the recoil and reliability of your weapons with upgrades, and above all, keep experimenting, because it's only through experimentation that you'll realise Far Cry 2's undoubted potential.

And it's also through experimentation that you'll experience the magic moments you'll not find anywhere else. Here's only a few of ours: Spotting the score of cockroaches darting about the floor of the APR HQ in town, evidence of Ubisoft Montreal's incredible attention to detail. Swimming in a ravine as the morning sun rises over the horizon, a breathtaking vista reinforcing the game's graphical credentials (if you've got a decent gaming PC and monitor you'll get the definitive version of the game from a graphical point of view - it ran fine in DX10 with all settings on Ultra High using our decent but not spectacular rig consisting of an 8800GTX graphics card, 2GB RAM, Quad Core AMD processor and Windows Vista). Driving through the Savannah wilds with a pack of zebras at your side (we only ever accidentally ran over animals, promise). Chucking a Molotov cocktail inside a heavily guarded building and watching the propagating fire technology flex its muscles as it sweeps in the direction of the wind, torching everything in its path. Using the grenade launcher to destroy a convoy and praying the charred metal doesn't fly in your direction. Completing the game's first act and feeling your jaw drop as the southern district map presents itself, transforming the game from what might have been a meaty 15 hour romp into an epic 30 hour adventure. Taking the time to scout, using the monocular to add ammo dumps, sniper spots, vehicles, health stations and turrets to your map before landing five head shots in quick succession from half a mile away. Stalking an unsuspecting enemy in the early morning rain, biding your time before sprinting in, sliding and taking your machete to his chest. Without experimentation we might not have experienced any of this. We've probably missed out on much more.

And yet, for all its brilliance, there are some glaring flaws that have crept into Far Cry 2's interactive innards that stop it from scoring that perfect 10. Much of this is to do with the AI. The AI on many occasions will do some hilariously nonsensical stuff that, rather unfortunately, reminds you that you're playing a game and not some virtual reality Arnie movie. They will often point the wrong direction while shooting, and yet still hit you. They'll also pump round after round into the cover they're hiding behind, perhaps thinking that their bullets will somehow make their way through that metal car door and into your flesh. When the car-driving AI spots you it'll automatically speed towards your position, often with nary a care for obstacles in its path. You'll hear exactly the same rev of the engine every time you're spotted too - a technique we know is the game's way of providing the player with an audio clue that a vehicle is inbound, but something that jars with the wonderfully unexpected nature of the rest of the game.

The save system differs from the console versions in that you can save absolutely anywhere and whenever you want. There are no checkpoints in Far Cry 2, at least not in the traditional sense of the term. Instead, you'll get a pop-up asking you if you want to save after you complete mission objectives, when you use the coach transportation system (only from a handful of coach stations dotted about the maps) or when you go to sleep using one of the Safe Houses. Or, as we've said, you can simply save anywhere.

You can save anywhere and anytime you want in the PC version

In the console versions, not being able to save adds to the tension and realism of the game (every death is a meaningful one - the antithesis of BioShock's Vita-chamber feature), but the problem is that sometimes you'll die attempting a mission and realise that your last save was about 40 minutes ago in that Safe House you passed en route to your objective. This isn't a problem in the PC version. In a way, being able to save at your leisure takes something away from the unique Far Cry 2 experience, but, on the other hand, it reduces repetition. While we think it will be hard to resist using it, you have the option to ignore the save anywhere function if you want that hardcore experience. Does this make the PC version better than the console versions? No, it makes it different. But it definitely gives the player the option to make the game easier.

The many guarded checkpoints will annoy some, but for others they will reinforce the feeling that you're never safe. Because the map is so big, you'll spend a lot of your time driving around. If you're going to stick to the road, you're going to run into at least three checkpoints along the way. Every soldier manning the checkpoints has a shoot first, ask questions later policy, too, making driving more a case of survival than sight seeing. The enemies respawn, too, so you can never once and for all clear enemies from that check point on that road you keep using to get to and from town. But these problems are well and truly put into the afternoon shade by the spell-blinding brilliance of what Far Cry 2 allows you to do, and how impressive it is from a technical point of view. That the game includes a brutal, class-based set of multiplayer mercenary deathmatch options and a truly superb map editor (complete with online sharing, editing and rating - oh, and it's better on PC because of the mouse and keyboard interface) makes it feel like even more of a complete FPS package.

Obviously if you're a shooter fan you should buy this game. A simple glance at the score should confirm in your mind, if there was ever any doubt, that Far Cry 2 is nothing but brilliant. But we're already looking to the future. Our minds are already spinning at what Ubisoft Montreal might come up with for the inevitable Far Cry 3. Just like your options when it comes to tackling a mission, the possibilities are endless.