Ico is a great game about the harmony of theme and mechanics.
The theme in Ico exists as story of a boy falling in love with a girl and trying to help her escape. These are also the goals of the player.
We discover Yorda as Ico does, and we are forced to drag her along if we are to proceed at all, with the motivation of, “What kind of heartless bastard wants to leave the poor girl sitting on the cold, stone floor to be accosted by shadowy things, etc.” Through the mechanics of pulling her arm and running ahead and catching and lifting her up, we are repeatedly tasked with helping Yorda where she cannot help herself. This endears us to her and helps develop feelings of empathy, which, ideally, grow to love.
You’ve read Tiamonster’s run-through of the game, so I won’t elaborate on how we mechanically achieve the other goal, freedom.
That’s really all there is. It’s a very well-made game. The devs set up the pins, and we knock ’em down. There’s no arbitrary gamification, as there would be in, oh, let’s just say, a Bioware title. We don’t need any gamified motives, because we automatically empathize with a suffering girl. There aren’t any numbers or dice, because we are either holding her hand or we aren’t. There aren’t any meters or plus/minus moral value assignments, because a game cannot tell you how you feel.