360: Dead Rising -I can get a lot of mileage out of that game
Wii: Super Mario Galaxy -like the 1984 original, I can play this one over and over.
PS3: GTA4 -May not be high on my must have list, but the series has always offered a ton of gameplay. Saints Row was awesome. GTA4 should be even better.
DS: Advance Wars D.o.R. -Strategy and Wi-Fi? Hell yes!