Galaxy is fantastic. It's endlessly better than Sunshine.
Other games you might like: RE4Wii, CoD:WaW or Medal of Honour: Heroes 2, No More Heroes, Zelda:TP, Fire Emblem RD,
Okami is definitely good on Wii. Widescreen is a plus over the PS2 version.
Mario Kart is THE multiplayer game of this gen so far. It's a must have on Wii imo.
Maybe save some money for upcoming games like Deadly Creatures, House of the Dead Overkill and MadWorld.