The first thing you need to know about Modern Warfare 2 is that the single player campaign is utterly fantastic and provides a rollercoaster ride that, while on fairly obvious rails, is so exciting you'll blow through it in no time.

The second thing you need to know about Modern Warfare 2 is that the multiplayer isn't as good as it used to be - on the PC version, at least - thanks mainly to the introduction of a new multiplayer framework. Dubbed IWNet, the new system has replaced dedicated servers with P2P match-making, zero mod support and far fewer customisation options.

In layman's talk that means that if you class yourself as a hardcore game player, the type of person who likes custom maps and playing with a clan, then you'll probably not like Modern Warfare 2 multiplayer.

The third thing you need to know is that that's not all there is to Modern Warfare 2 and that a new mode, called Special Ops, has been introduced for those who prefer to play co-operatively. It's this last and most new addition to the series which is the real stand-out success of the game, offering players a variety of self-contained missions and unlockable awards.

This isn't your standard run and gun, either, as the Spec Ops mode includes some really inventive missions. Our favourite is the one where a player is a soldier who is trapped behind enemy lines and who must make it to the LZ as fast as possible, on foot. The second player covers him from the air with a thermal imaging-enabled artillery platform. And that's just the start, as there are plenty of stealth and assault missions in Spec Ops mode too.

This huge amount of variation in the co-op levels (which can also be played single player) is also matched in the single player campaign, too, and the story, which revolves around an ultra-nationalist Russian movement trying to terrorise and invade the US, is equally unique. In just the first few levels you'll go from climbing up the sides of glaciers and covertly infiltrating bases under the cover of a blizzard to chasing informants across Brazilian rooftops. And that's all before the fight really breaks out in suburban US.

The combined result of all this is that the single player campaign of Modern Warfare 2, while a bit short, is incredibly fast-paced and offers something for everyone. It's like a game adaptation of 24, but with Jack Bauer's brain and gravelly voice jumping into the mind of a number of different soldiers.

Unfortunately, though, the multiplayer is a bit of a letdown, and although the actual game itself is really good, the IWNet framework is constant bullet in the backside. Simple things have been blocked, like text chat in lobbies (though microphones are still allowed) and the ability to customise the length of matches and levels. Every ten minutes you're being booted back to the lobby screen, it seems.

In the end, though, gameplay manages to win out this time around and while IWNet is definitely a hindrance, it isn't quite enough to spoil the game as a whole.

Modern Warfare 2 is just too good and the expanded multiplayer arsenal and skillset, which now offers everything from remote missiles to heartbeat sensors, is enough to keep you playing in spite of the problems.

Let's just hope that IWNet doesn't stick around for other games that can't blind us with such brilliant quality!

Get Call of Duty: Modern Warfare 2 from just £32 at the Den of Geek Store:

• Call of Duty: Modern Warfare 2 (PC DVD)
• Call of Duty: Modern Warfare 2 (Xbox 360)
• Call of Duty: Modern Warfare 2 (PS3)