So, here it is - the most eagerly anticipated game of 2009. You'll have to forgive me if the following preview is somewhat scattershot in nature, as I'm writing it at a height of 10,363 miles above the Atlantic, and my plane is getting battered by turbulence. There's also the fact that there's an awful lot to talk about. Last night Infinity Ward showed off Modern Warfare 2's multiplayer mode for the first time, and though the build on display was a beta limited to three maps, I could easily fill four articles with impressions of the things I saw.

In broad terms, MW2's multiplayer is very similar in appearance to its much-loved predecessor. There's a wide selection of real world weaponry, a brutally swift pace, and a frame rate as smooth as blended fois gras. However, it soon becomes apparent that Infinity Ward has actually been quite radical in its attempts to innovate the gameplay we know so well. The basics are still there, but the overall experience has become more diverse, more complex and even more frantic than before. There are few journalistic cliches more tired than "A is like B on C", where "A" and "B"are two comparable objects and "C" is some kind of recreational drug, but here it really does ring true. This game is a crazier, more colourful version of its former self, and while some of the changes may upset hardcore purists, most of you are going to be thrilled by the experience on offer.

Take killstreak rewards, for instance. As with CoD 4, Modern Warfare 2 rewards players who manage to kill several opponents in a row without dying. Last time there were just three prizes to earn, but now there are enough to stock up a particularly blood-thirsty gameshow. The reward for three kills is still the UAV, a radar tool that reveals the location of your opponents, but if you notch up four scalps you'll get a care package - a friendly airdrop that grants you a random reward. Once activated, the player throws out a special grenade that emits red smoke; a few moments later a large crate will plummet from the sky. The box might contain ammo or health, but if you're lucky it'll contain one of the later killstreak rewards - the big toys that will cause even the hardest of veterans to soil their khakis. You may have never summoned the helicopter in CoD 4, but this time everyone gets an outside shot at the upper-level firepower.

What kind of toys am I talking about? Well, the five kill reward is a Predator missile. The player whips out a laptop computer and the screen suddenly shifts to a black and white overhead view of the map - the rocket's perspective on the battle, as it were. You guide your descent with the left thumbstick, aiming for the red squares that highlight your enemies. Tug the right trigger, and you'll plummet to the ground in a second, decimating anyone beneath you. Higher up the killstreak chain you'll gain access to brutally efficient sentry guns that can be left to guard important points on a map. You'll also be able to summon several different flying vehicles - including attack helicopters, MH-53 Pave Lows, and the dreaded AC-130 gunship.

Somehow, Infinity Ward is crafting an even better multiplayer experience.

Because there are more of these rewards, and because they are so lethally efficient, they have a greater degree of effect on a given match. These new breed of killstreaks have different strategic implications: Care packages can be grabbed by anyone, friend or foe, so it's important that you deploy them wisely. The more powerful helicopters will virtually force the opposition into hiding, but they can be shot down with rockets or by summoning another vehicle that can attack them. And at the other end of the spectrum, there are now consolation prizes given to people who are getting creamed by the opposition. Get whacked enough times and your chosen Deathstreak perk will kick in - a bonus that's designed to get you back into the match. One choice allows you to mimic the class setup of the person who killed you, while another ensures that you respawn with an extra dollop of health.

You see what I mean about there being a lot to discuss here? I've just spent three paragraphs talking about the killstreak rewards, and yet these are only one of several new features that Infinity Ward has brought to the table. Perhaps it's just me, but there seems to be a slight air of excess about Modern Warfare 2. Aside from the new arsenal of tools and weapons, there are also a ton of new in-game challenges that reward you for pulling off particular feats during a match. At times it seems you get some form of XP reward every 10 seconds. Killed the bloke who snuffed you last time? Have a bonus. Shot someone who was building up a fat killstreak? Have a bonus. Murder three different people with three different weapons? Have a bonus.

As a result of all this, it seems that most players will level up at a faster rate than before. A gauge at the bottom of the screen shows you how close you are to the next rank, and every time you make a grade, you'll unlock something new. At level one you're limited to playing as one of three pre-set character classes, replete with set perks and weapon loadouts. As soon as you hit level four you'll gain the crucial option to build your own class, and you'll also be allowed to play with things like riot shields and your first sniper rifle - the unbelievably sexy Barrett .50 cal. At higher ranks you'll gain new weapons and equipment, plus the ability to add clan tags, or to customise the order in which you gain killstreaks. At every stage of the game you'll also win Street Fighter IV-style name tags that can be applied to your character profile. The first is "F.N.G" - an acronym that will make sense to everyone bar F.N.Gs themselves - but later titles will presumably let you boast about your skills and style of play. This isn't a world changing addition by any means, but it's yet another way for players to tailor their game.


Now, let's talk about guns. As you might expect, there are a lot of firearms in MW2, and while I certainly don't have time to mention them all, it's worth discussing some of the ones that stand out so far. The FAMAS is one of the three weapons available from the get-go, a French assault rifle that effectively replaces the M-16 from the last game. It fires three-round bursts, is very accurate and serves as an extremely versatile tool - so I expect most people will choose this as their early favourite. Another popular choice will be the aforementioned Barrett sniper rifle - a gun that was previously only unlocked at rank 49. By default it comes equipped with a heartbeat detector - a screen clipped to the side of the gun that gives a vague indication of nearby hostiles and friendlies. To be honest, I suspect this add-on will work better with close range weapons, but the gun itself is hugely fun to use - especially when you headshot some fool and get the "One Shot, One Kill" challenge.

Riot shields are one example of the way this game departs from the more down-to-earth flavour of the first Modern Warfare. If you so choose, you can now swap your primary weapon for one of these bulletproof badboys: when it's active you will move slowly, your vision will be partially obscured and you won't be able to fire a weapon, but you'll also be largely invincible to standard fire - unless someone flanks you or chucks a grenade over your head. It's incredibly confusing and rather intimidating the first time you come up against someone with a shield, as you suddenly have to change all your tactics. I utterly failed on my first attempt to deal with such an opponent: I backed him into a corner, uselessly emptying a FAMAS clip at him, and eventually started swiping away with my knife. And when that failed, and my spirit was broken, my foe switched to his dual-wield machine pistols and blew me away.

I have absolutely no doubt that some people will hate the shield-bearers, but Infinity Ward is 100 per cent confident that they're a balanced part of the game. When the shield is up you can't attack, and when you go on the offensive you'll have to do so with a secondary weapon - but on the plus side, you'll have your back covered. While we're on the subject, there's now a huge variety of secondary armaments. You can still use pistols, which are once again the quickest guns to equip, but you can also take shotguns, machine pistols or grenade launchers. On a similar note, you can now take a whole bunch of things to battle in place of your grenades. There are throwing knives, semtex (essentially a sticky grenade) and, perhaps most unusually of all, tactical insertion markers. The latter allow you to spawn wherever you like on a map: set one up deep within enemy territory, and you'll be able to return to the frontlines almost immediately after a death.

Will features like these unbalance the carefully weighted brilliance of Modern Warfare's multiplayer? It's possible, but let's have some faith in Infinity Ward. These guys know what made the first game so good, and they've been playing seven shades out of their new baby. If they're going to allow people to choose their spawn point, or to equip an assault rifle with both a silencer AND a red-dot sight (yes, you can), we should believe that these options will work without being overpowered. It's too early to tell, of course, but on the basis of what I played on Tuesday night, I can certainly tell you this: the multiplayer in Modern Warfare 2 is utterly sublime.

Meet the riot shield - your best friend and worst enemy.

Why is it so good? In precise terms, I really can't say. After the preview event a few of us weathered hacks were discussing the game and why it works so well, but we failed to pinpoint the single ingredient that makes the magic happen. Perhaps that's the point - it's a lot of things. It's the sheer effortless style with which it delivers the thrills - the oh-so-slick smoothness, the speed, the rattling gunfire. It's the detail of the level design - the favela map with its abandoned barber shop, colourful propaganda and a pair of rusty goalposts in a dusty yard. It's the utter rush when you launch a grenade into a clump of people and score three kills at once, or when you shoot through a wall and cap the guy crouching behind. It's the knot of tension that forms in your gut as you plant a suitcase bomb, the terror as three enemies rush your position, and the whoop-out-loud triumph as the explosives blow the four of you into oblivion.

On top of all this, in a quite different way, it's the realisation that competitive multiplayer is just one part of the deal. We've seen barely anything of this game yet: there's a full set of co-op missions, and on top of that, there's the entire single-player campaign. I mean, who doesn't remember the main story in CoD 4? That incredible bit with the nuke, the wonderfully dark AC-130 section, and the bloody drama of the whole end sequence? Hell, even the Ferris wheel section, the one battle that pissed everyone off, even that section was pretty memorable. I have no idea what awaits us this time around, but I know that I can't wait to find out. Will Modern Warfare 2 be the best game of 2009? Let's put it this way... you wouldn't want to bet against it.

Call of Duty: Modern Warfare 2 is due out on Xbox 360, PS3 and PC on November 10.