I'm not exaggerating when I say I think this was the greatest game to come out of the Xbox/PS2 generation. Honestly, as a whole, it may be the one of the greatest games ever made as far as I'm concerned. A lot of it was derivative of Zelda, but it also improved on the formula in almost every way. That and the artistic style and setting was just fresh and amazing. There is a ton of value there for $20.
And you just reminded me to check out the DS game.