The one game that I will remember the PlayStation 2 for is, of course, Shadow of the Colossus. I don't think that there's any game on the PS2, Xbox, or GameCube that can top SotC for pure enjoyment.
A couple of my friends don't see what's so great about Shadow of the Colossus. They say that the controls are too simple, that the graphics aren't as good as people say, and that the gameplay itself is just boring. On the plus side, none of my friends have said anything negative about the game's soundtrack. Do yourself a favor and buy it. =D

I feel these friends of mine have missed the whole point of the game. It's not about just killing the bosses. The developers have left much of the story up to speculation for a purpose, just like they did for ICO. They wanted us to put our own emotions into the game. This way, we would be more connected with the Wanderer and his adventure. They leave it up to us to decide who the girl is. And ultimately, it is left up to us to imagine the lives of the game's characters after the credits have rolled past.
You just don't get that kind of immersion from games that straight up tell you what the characters are feeling.
The personalized emotional investment that SCEI allows to have for the characters in Shadow of Colossus is reason enough for me to claim that it is the best game of the PS2/Xbox/GCN era. It doesn't hurt that the game is also a lot of fun to play.