Combining unique graphics with familiar, but wonderful and memorable gameplay.
Next, the plot. You play as Okami Amaterasu, the "origin of all that is good and mother to all" reborn after dying 100 years ago, whose quest is to restore it's full power by retrieving the reality-bending powers known as the 13 Celestial Brush Techniques, and rid the world of the darkness that's plagued the land. You'll be surprised at the amount of plot twists and character development that can be found in this game. Each character just shines with his or her own special personality or backstory. The main problem for Amaterasu is that the people's belief in the Gods has waned since Ammy had last walked the earth, thus his/her power is not what it once was (and not to spoil anything but later on in the game, you'll be surprised how powerful Amaterasu used to be).
What's worth as much praise as the great God Amaterasu is the game's music. I've never heard such epic Japanese-influenced orchestral music in any game before, and it's sad that it took sixteen and a half years for these ears of mine to hear such an amazing soundtrack. There's not one scene in the game where I thought they should've used a different track, and if your opinion on the music is the same as mine, then you'll know they saved what may be the game's best song for the last boss.
The game's dungeons are somewhat scarce, but most of the adventure takes place outdoors anyway, traversiong across the land of Nippon restoring it to it's former glory. What's a little unfortunate is that most of the dungeons, when seen individually are rather short and uneventful, but at the very least, no two are alike. With this game being so often compared to the Zelda series (for numerous reasons, one being the silent protagonists), this particular comparison of puzzles and dungeons is like comparing one of Okami's minor weaknesses to Zelda's biggest strength; very unfair, yes, but unavoidably true. But that, to me, is a small price to pay for a game that's overall the most epic thing on the PS2 since Shadow of the Colossus or the Kingdom Hearts series.
The game's bulk revolves around Amaterasu's powers of the Celestial Brush. True to the game's graphics, the use of this ink-brush works to add more to or restore the game's world. A simple circle around a withered tree will restore it to a cherry tree full of perfect cherry blossoms, and then make a loop-de-loop to blow all the leaves right off with wind summoned from said loop. Most of the techniques involve mainly just drawing a line from the source to the target, but hidden throughout the world are upgrades that help both inside and outside of battles. It also feels like the game makes plenty of use for each of the techniques no matter where you are in the game, successfully reminding you that they're still loaded in Amaterasu's tail (which is what it apparently utilizes to use the Celestial Brush powers). Heck, even if there are no puzzled that need solving, it's still a little fun just to use the moves out on the unexpecting people of Nippon!
When it all comes down to it, if you love the adventure genre and want a game that you know you'll still play even after getting the next-gen consoles, Okami for the Playstation 2 is a dead-set example of why backwards compatibility exists. And if you're a Zelda fan waiting for Twilight Princess, not only will this game hold you out, but you just may take a quick break from the game just to come back to this one.