Considering how great this game is and how much I loved it, I must declare its sales to have been a bit of a let-down. It isn't that it sold poorly for a GameCube game during its time so much as that it really should have sold a lot better than it did. This game is still one of my favorite GCN gaming experiences.
Hardcore gamers that followed the game's development knew that the title was originally a Nintendo 64 project before it fell back a generation with some major upgrades for the GCN, and it does sort of show in its visuals, but that isn't to say that the game looks bad, as it was still better looking than a lot of other games at the time. It's just that it wasn't pushing the hardware any. I didn't complain any, though, and the game does sport some nice FMV sequences.
I felt that the voices didn't disappoint any; satisfied with the acting and sound quality and pleased to see authentic Latin where appropriate. I don't have any complaints about the music, either, and one of my favorite tunes from the generation comes from this game.
I've seen this game compared to Resident Evil, but that really isn't a very good comparison at all since each game attempts to scare players very differently. Eternal Darkness is more of a psychological thriller than a game of cheap spooks, evident in the games unique sanity meter. The characters' experiences often have detrimental effects on their sanity, which can result in all sorts of hallucinations, so the player can't ever completely trust what they are seeing and hearing, as it might not be real.
Most of the story takes place in the past, prior to the events involving the actual main character, and is experienced one chapter at a time as she explores the mansion, solves puzzles, and reads. During the course of the game, the player will thus take on the roles of several different characters across history and across the world. The game uses architecture authentic to time and place, and characters use weapons, armors, and clothing from their respective locations and time periods.
Besides the sanity meter, the game deals with magic a bit differently from other games. As the player progresses through the game, the player finds magical runes, scrolls with which to translate them, and circles of power around which to place them in various combinations to create magic spells, sort of like forming short sentences with runes that each represent different words. Further, magic is aligned to one of a handful of "ancients", powerful god-like entities warring against one another, each strong against one and weak to another.
Early into the game, one character takes up an artifact of one of the three main ancients, starting on his path as a pawn of that particular ancient, but the player chooses which one that is. This effects what enemies are encountered (including bosses) as well as the cinematic sequences and ending. After beating the game, the player could play through a second and third time, each time choosing a different one. After a third time through the game, a fourth ending follows.
I don't normally replay games, these days, but I did play through this one thrice in a row, which I think says something about this game. It isn't overly lengthy, as I think that I beat it in about three hours or so the second and third times through, but that makes it no shorter than most Resident Evil games. I highly recommend this game.