Official story and features:
"You are John Raimi, a disease-control agent with the federal government, on loan to an elite counterterrorism unit. Your team is sent to investigate the shadowy Volks Corporation. When the operation goes horribly wrong, you are captured and subjected to a ghastly experiment that rips your spirit from your physical body. You now roam the halls of the Volks Corporation compound as a spectral phantom, using your powers to scare and possess any human or animal that crosses your path.
Players must search for their physical body, which is mysteriously being kept alive somewhere in the enormous complex. Players won't always be alone though--as they explore, they must collect the energies of indigenous spirits to help unravel a mystery and build their own power. Some will help ... but beware, for not all the spirits are friendly. Prepare for a first-person adventure with a spectral twist!"
Story from Nintendo's site
"- Explore the compound as a ghost, then possess more than a dozen unique character types using their weapons, equipment, skills, and even memories, to complete your goals.
- Possessions range from soldiers with guns to dog- and mouse-like creatures that can perform specialized physical tasks. Choose different characters and see the world in different ways.
- Travel through the human world virtually unseen, using your abilities to slip through cracks, interfere with electronics, move objects and more.
- Face challenges from two unique angles: as a possessed human or a lurking spirit hunting its prey.
- Prepare for death matches with the dead in all-new multiplayer modes that combine first-person combat with unique ghost and possession mechanics."
Features from Nintendo's site