Unique, fun, and underrated. ED is one of the GC's best games.
The time periods you traverse are all unique and interesting in their own ways often with slightly different gameplay feels that keep the game constantly fresh. Near the end the game gets a bit repetitive though which is annoying eapecially on the second and third times through (which there are incentives to do), but not enough so that it detracts.
The combat system is heavily criticized but I found it to be intuitive, simple, and effective, except for in a few situations. The magik system is also simple, in some peoples opinion to a fault, but for me it got the job done.
The sanity system is what made this game. You get a sanity bar along with the ones for magik and health and it is equally important. As you see and kill enemies you loose and gain sanity. With low sanity the game is harder, scarier, and such. With low sanity also comes the games highlight which are the sanity effects which mess with both your in game character but you as well.
One fault would be how easily some of your characters become fatigued but it doesn't detract too much and it is actually more realistic. And you can also say the graphics are a little cartoony and plain.
One of the top three on the GameCube.