"Geist" means ghost in German, so you will not be surprised to learn that Geist, the video game, is all about being a disembodied spirit, knocking on the walls and frightening nervous guardsmen and generally going bump in the night. So why not simply call it Ghost? Two words: Demi Moore. Two more: Patrick Swayze. Two more that count as ten: Whoopi Goldberg.

The game is terrific fun and not at all maudlin or weepy. It is carefully and thoughtfully imagined, and it is often startlingly original, so you will forgive it the occasional misstep in execution.

Yes, you will. Video game developers are timid. Their moments of courage must be praised, or soon we will all be up to our necks in football and RPGs, with new releases everywhere but nothing to do with our thumbs. If you fail to encourage video game developers when they break new ground, you deserve to be locked in an attic for a month with nothing but bread and water and a copy of Mega Man 8.

So, Geist. It is flawed, but it is also brilliant, and in the end its brilliance outshines its shortcomings. Here is how it works.

Your name is Raimi, possibly in honour of the guy who directed The Evil Dead. You are a biochemist. One day, you are summoned to participate in a raid on the headquarters of the Volks Corporation, which are in the south of France and appear to be surrounded by prime vineyards. An old friend of yours, an expert in chemical weapons, is apparently being held captive, forced to perform unethical experiments with dire consequences. It falls to you and a team of special-forces soldiers to a) carry out the rescue, and b) put a stop to any tomfoolery you encounter.

The Volks Corporation is a weapons company and your bosses are generally OK with that, but they are not OK with with the shadier stuff they are hearing about, which seems to involve a) viruses, and b) demons.

The raid begins. You and the soldiers drop from helicopters into a firefight. The soldiers pull out their automatic rifles and start shooting. You hold back, being a civilian armed with just a pistol, but the soldiers offer you a few words of friendly encouragement and before you know it you are shooting Volks guards as if you've been doing it for years. All the action plays out in first-person perspective, with controls that will feel very familiar to anyone who has played Halo. It is a little underpowered, on account of your wimpy gun, but the aiming and the running feel good in the hands, and you note to yourself that this could turn into a pretty good shooting game with a weapons upgrade or two.

Then you get killed. A bullet nails you somewhere in the abdomen, and you fall down, and everything goes blurry and then it goes dark, and suddenly you find yourself in a beautiful meadow, comforted by a gentle voice that seems to come from everywhere and nowhere at once. The voice tells you that this is your home now, and see that bunny over there? You can possess it if you want. Hoppity hop!

Then the meadow crackles and falls apart, as if they were computer graphics and the computer showing them were running Windows. It was all a virtual-reality brainwashing environment. You don't really live in a meadow.

You are still dead, however. Apparently the scientists at Volks have learned how to trap spirits, and are planning to use them as super-soldiers. You, being a convenient corpse, are their latest experimental subject. But you escape, and now you roam the corridors unseen, seeking answers and revenge.

You can possess inanimate objects like garbage cans and mop buckets. You can possess people and animals, if they are frightened enough. Luckily, there is nothing like a haunted mop bucket for working a person into a frenzy. Shortly you are hopping from body to body to bucket with ease.

When you are in a body and that body has a gun, the action is frenzied first-person shooting. The shooty bits are fun, but that sort of thing has been done better elsewhere, with graphics that run with smoother frame-rates.

But when you are trying to figure out what to do next, the play is gentler and more puzzling. You need a door open, and the man with the key is over there. How will you frighten him? When you succeed, you realize you are thinking like a ghost. You feel your own powers and chafe at your limitations. You are not the person you once were. You are more, and less, and at every moment you feel as if you might dissolve in the mist. It is frightening and delicious, that mindspace.