The millennia-spanning saga plays out through a series of flashbacks related to the Tome of Eternal Darkness. The grisly book depicts the struggles of numerous explorers throughout the centuries whose fates became intertwined with the Tome -- they all become embroiled in a battle against the Eternal Darkness, Ancients who seek to take dominion over the entire Universe. Quoting Poe before the game even begins hints at Eternal Darkness's literary pedigree -- the story is top-notch, expertly written and superbly narrated. Piecing together the plot as it hops, skips and jumps through time is exciting, and few games can match the intrigue and atmosphere Sanity's Requiem develops.
Though the story creates an appropriately creepy atmosphere all by itself, the Sanity Meter is where the real scares come from. As you take on the roles of the various discoverers of the Tome of Eternal Darkness, hordes of rotting zombies and other freakish creations will come to claim your life. Because the game's characters are depicted as fairly normal people, the presence of the undead has a mildly negative impact on their sanity. The lower it gets, the more unsettling the game becomes.
Gameplay in Eternal Darkness is a mix of exploration, puzzle-solving and combat. It's easy to spot traces of classic point-and-click adventures in Sanity's Requiem, as many objects in the environment prompt you to examine them, and the majority will offer a deeper description of the object with another button press. Examining your surroundings is, obviously, an important part of the puzzle-solving process. The puzzles generally aren't particularly challenging, but they often involve combining various objects or figuring out what to place where to activate a secret passage, open a door or make some ancient device awaken from its long slumber. Eternal Darkness also draws inspirations from the classics such as Raiders of the Lost Ark -- there are plenty of swinging axes, blow dart traps and other hazards to liven up your adventure. And, of course, there are those pesky undead walking around.