Alright, I admit it. I'm a little late to the party.
I played Okami only a few months ago. (Sue me). But damn, did it leave an impression on me. Anyone who has played it knows why. It's friggin beautiful. The art direction was brilliant (Japanese watercolor? Seriously?), the music was actually good ( I find that too many games get away with crap music), the story was interesting, as were its characters. Who can forget Mrs. Orange "Raging Demon"-ing her stove to whip up some cherry-cakes for you? The incredible battle with the demon Orochi in the cave shrine? Or Nine-tails on Oni-Island? The sense of awe and warmth at Ammy's recovery, thanks to Issun, during the final battle with Yami? Whats more, the gameplay is solid, if not a bit easy. But hell, I can forgive ease; it's an adventure game, after all, not a hardcore action game.
What makes Okami such a classic is the fact that the game is a brilliantly polished "whole-package" of a game. Every major aspect of the game, control and gameplay, sound, story and pacing, characterization, is all done beautifully. It is what I would consider the adventure game "ideal". Okami had everything that it needed to do the be a good, memorable game, and it executed it wonderfully.
What this amounts to is a gaming experience I have not witnessed since my completion of Zelda, A Link to the Past, back in 1994. Okami is now the game I use to compare all other games in this Genre, that's how wonderful it is. If you still have a PS2, I highly, highly encourage you to get this treasure of a game. (It was ported over to the Wii as well, but I heard the port was kinda choppy and unresponsive regarding the Wii-mote controller. I haven't played the Wii version, so I can't say for sure).
Of course, it's not perfect. But the minor gripes feel so insignificant compared to the whole of the game that I may as well not even mention them. So I wont. Buy Okami if you haven't already. Buy it. Now.