Gran Turismo 4. It's quite simply brilliant.
Shadow of the Colossus
Probably the most impressive and powerful game I have played. Not for everyone though, not enough non-stop action for some people. But no other game has sucked me into its universe like that before. The mood/atmosphere is unparalleled. If that is something you can appreciate, you can't go wrong.
God of War I or II. The game has several elements from different game genres. Elements of RPGs, strategy, and action are all combined together. Plus, they have good replay value. (Different costumes, unlockables, harder difficulties.)
God of War I or II. The game has several elements from different game genres. Elements of RPGs, strategy, and action are all combined together. Plus, they have good replay value. (Different costumes, unlockables, harder difficulties.)
Highly endorsed. Also check out ICO, the game which preceded Shadow of the Colossus. Similarly engaging, heavily atmospheric, and sports the same "design by subtraction" philosophy. It doesn't hurt that the two games are linked story-wise too.
Fumito Ueda is a game-design god. I can't wait for his PS3 games.