This is actually a good question. Last gen had many good games, but few of them were something special. That said, I guess my pick is Twilight Princess, with Mario Galaxy being a close second and Resident Evil 5 being third.
Bet with Teeqoz for 2 weeks of avatar and sig control that Super Mario Odyssey would ship more than 7m on its first 2 months. The game shipped 9.07m, so I won