Okami
If you have a PS2 and don't play Okami, you're a bad person. It's simply a fantastic game. The graphics are stunning - I don't care about the GE Force 8800 or the new current generation of high definition systems, Okami is the best looking game I've seen, thanks to the great art style and amazing cel-shading technology that makes it look like a living watercolor painting. This is an opinion of course, if you'd rather look at super high-def ruins in Gears of War, that's just fine. The game also has great music, although I can't say all the audio is good. Okami's main flaw is the voice acting - it's text based, and instead of silence or some beeps, you get garbled snippets of voice (like Banjo-Kazooie) that's tolerable at first but gets very annoying after long bouts of extended exposition.
It's not just great because of its aesthetic qualities though, it IS a video game, and a good one. I can say without doubt it is the best Zelda-style action adventure that isn't actually a Zelda game I've played. It's easy, but still fun, thanks to the Celestial Brush, which you use to draw your special attacks and tools instead of having to sort through an inventory. The different brush powers are all easy to learn and remember, and they give Okami a unique flair to the traditional exploring and combat. The dungeons are more focused on using your powers to advance forward, the puzzles are less Zelda-style solving something to open a door and more using your techniques and platforming skills to reach that door. The combat is a little simple, but still cool thanks to slick attacks, a variety of weapons, the use of the brush techniques, and interesting enemy design.
The story should also be mentioned, I wasn't expecting a lot, but it's actually quite good. The character development is great and there are some cool twists and turns, and it's all enriched by the Japanese mythology that surrounds it. Overall, Okami is a cohesive, beautiful work of art and it's a damn shame no one is playing it.
