Okami = 10/10
I actually picked up the Japanese version of this game the day it came out over here.
I can easily say that, unless you hate games, you will love this game.
It is so extremely well made, everything from the graphics, and sound, to the game flow and intricate intertwining of a massive and charming adventure, with really cool action packet battles (the depth to which the brush is utilized is amazing, and extremely intuitive).
As far as I see it, this is one of the greatest games to come out this generation, and deserves to sell boat loads.
People will undoubtedly compare it to Zelda on the GameCube due to the somewhat similarity in cell shading, and overall massive scale. However, in all honesty I found Okami to be infinitely more entertaining, original, and engrossing than Zelda.
If you buy any PS2 game before moving onto the next generation, this should be one.