Splinter Cell has become one of the most important videogame franchises in recent years and helped redefine third-person stealth titles.

The fourth outing is the most radical change yet - not because the gameplay mechanics have been altered dramatically but because the element of choice in your actions has become inescapable.

Double Agent explores the moral complexity of a spy's life - having to make life or death decisions when the ethical outcome is not always clear.

The narrative of previous Splinter Cell games has always been a mix of the dynamic and the hackneyed but in Double Agent the balance is to the former rather than the latter.

The weakness in computer games is traditionally the realisation that your sense of choice and of freedom actually leads you to the same conclusion no matter which path you take.

But in Double Agent you actually feel as though your decisions count.

The first level is a primer for the game - infiltrating a geothermal plant in Iceland with a young sidekick.

The game's designers have generated real atmosphere and a sense of place.

Throughout the game you get to explore parts of Shanghai, Iceland, and large ships, tankers and office buildings galore. Variety of actions in these locations is also impressive - rappelling off a skyscraper in Shanghai is a real highlight.

Visually the game is stunning, using the high dynamic range of high definition gaming to great effect.

The musical score is spot on, rising and falling in tempo with the slightest change in action.

At the end of the first level Sam is left rock bottom with two great losses in his life. This emotional turmoil then permeates the rest of the game and sets the scene for the moral choices you must make as Sam Fisher.

Early on Sam finds himself in the company of a group of terrorists called the JBA and in these levels there is a range of tasks to complete with a number of sub-objectives.

The tasks are engaging and give rise to plenty of opportunity to explore the landscapes/environments in which they are set.

This is old school stealth - creeping around with high tension and high stakes.

The control mechanism of Splinter Cell remains largely intact - the developers have also worked hard to ensure that the fancy moves and cool equipment get used and while the signposting might irritate some, it does make the game feel more rounded.

The big development of the title is in the use of Directed Moments.

These are interactive situations that force you to make a difficult choice in a tense situation. The first is having to decide whether to kill a helicopter pilot: If you kill him you gain the trust of the JBA but an innocent man dies.

If you do not, you lose the JBA's trust, but grow the confidence of the National Security Agency and keep a man alive.

They are interesting choices - not least because as video gamers we are used to arbitrarily killing characters with little thought to consequences.

As the game progresses, the decisions get tougher and tougher leading to decisions that could cause the deaths of thousands of innocents.

Ubisoft has managed to inject real originality and innovation in a five-year-old franchise and produced the best stealth game I have played to date.

And the multiplayer element is still one of the best twists on online action around.

Snake has got his work cut out if he is to top this game in the next Metal Gear game for PlayStation 3.