When I played Eternal Darkness, I was totally blown away. This game has depth, an intelligent plot, and is scary as hell! This is not a typical game on any console, but especially not for GameCube. I found myself playing this game all alone one night, absolutely scared to death, jumping every time the a/c kicked on, but totally unable to turn it off!
It isn't the longest game ever, I beat it in around 15 hours, but that is balanced out somewhat by the fact that you are supposed to beat it three times, with three different alignments, red, blue, and green. Each time you play through it, things change, sometimes noticeably, sometimes not so much.
I found the boss fights somewhat frustrating, mainly because you ended up doing the same thing over and over until they finally died. But they looked darned cool doing it!
Graphics were pretty good, surprisingly real in the cutscenes, only slightly odd during gameplay. Things like character's hair, or their gaits were slightly off at times.
I also really like the puzzles. They were tough enough to bear thinking about, but not obscurely difficult enough to get truly frustrating. And they are a welcome balance to the hack and slash bits, which was also really well done.
By far the coolest part of this game is the sanity meter. I had always wondered about the main characters in horror/survival games. How do they keep their cool? You wake up in Raccoon City and there's zombies and stuff everywhere, and you say, "oh well, where's a rifle?" and get on with it? Well, in this game you don't do that. In fact, you go steadily crazier as various nasty creatures see you and you see them, until finally you are crouched in a corner going "this isn't happening..." How cool is that?
If you love horror games, this game is totally for you. It is definitely one of the most interesting and original GameCube games I have ever seen.