Animal Crossing on GC by a looooong shot! At least 400 hours. I remember all those days running around doing odd jobs, fishing, buying furniture, redecorating, playing NES, and basically just hanging out... ahhh, my complete Citrus furniture set, complete with wallpaper, flooring, and about 10 lemon and lime chairs...
can't wait for the Wii version How about some connectivity with the DS? Transfer your town to AC:WW and play on the go plz?
This gen, defnitely Gears of War. Such a great game! Haven't played for a while, but I played 3-4 hours a day for weeks when it came out! Still have the odd match every couple of weeks.