What games have defined this generation for you and why?

[mmnin]

Wii Sports: ushered in the Wii phenomenon
Zelda Crossbow Training: Justified the Light gun aspects of Wii
Elebits: Showed the creativeness that could be had with Wii
Mario Galaxy: Showed how Wiimote can be used in interesting ways even in bettering current genres traditionally

Others to come eventually...