Shadow of the Colossus is an adventure game set in a fairytale land of castles and great ruined temples. It is about a girl who died and about the teenage boy who pines for her resurrection. It is about 16 enormous monsters who roam the countryside. It is about swords and arrows and riding a horse. Its raw materials are pure video-game boilerplate.

The surprising thing is how original it all feels. To play Shadow of the Colossus is to be enraptured and amazed, to feel yourself empathizing with (and maybe even tearing up over) pixellated characters who never speak an intelligible word. It is a video game with a soul.

It begins with a long video clip, which shows the teenage boy riding his horse through forests and up a narrow mountain path, across fields and an impossibly huge bridge, to a temple in what looks like the end of the world. Everything is stark and quiet. The sun shines with a bright golden light that somehow feels cold. In the temple, the boy carries the dead girl up a huge staircase and places her on a stone altar. Please, he asks the spirits, bring her back. The spirits tell him he might get his wish, if only he will kill all 16 of the enourmous monsters out there in the countryside. They warn him that he might not really want what he's asking for.

He is not dissuaded. He holds his sword up in the sunlight, and the reflected rays converge on a spot in the distance, and he knows that he will find the first monster in that spot. He climbs back on his horse and rides off to fight.

As we ride, steering the horse and periodically holding the sword up for directions, we find ourselves stunned by the scale of the place. We ride for what must be miles and miles, past hills and rocks and that otherworldly bridge, coming at last to a little cliff. We dismount, we find a way to cling onto vines and hang onto rock ledges, and we climb. At the top, a beast larger than anything we have ever seen in a game is stomping in circles. It is larger than buildings. Its every step makes the earth shake. It is not at all interested to see us.

Our sword tells us that the colossus has a weak spot high on its body. The challenge is to find a way up there. And this, this business of finding a way up the colossus, is the heart of the game. We run between its feet looking for something to grab onto, trying to avoid being crushed. We try climbing the neighbouring cliffs, hoping we might be able to jump from there onto the beast's head. We wonder if the bow and arrow might be useful.

It's a kind of puzzle. Eventually we figure it out, and we plunge our sword deep into the glowing weak spot, and the colossus falls down like a mountain. A moment later, we're back in the temple, and a shadowy, ghostly figure is standing beside our prone body, its head tilted at an angle that asks a one-word question: Why?

The truth is, we don't know the answer. What did the colossus ever do to us, anyway? Who are these spirits who want all the monsters dead?

As we fell one monster after another, that ambiguity grows. It becomes wrenching, landing that last blow with the sword, because we know yet another magnificent creature is about to meet its end, and because we're ever less sure we should be out here at all, trying to bring back the dead.

Questions of Good and Evil get no play here. Shadow of the Colossus is too subtle and too sophisticated for that. What does play is a relentlessly gripping adventure, where we're never sure what's happening or why, but where we can't turn away, and indeed can't stop ourselves from advancing the action. This is one of the best games of the year.