Fifteen years to the day, Super Mario Sunshine released to critical acclaim on August 26, 2002 (July 19 in Japan). For the first time in series history, and thankfully last, several cutscenes were fully voiced acted. Mario himself didn't speak at length, but Princess Peach, Bowser, and the newly introduced Bowser Jr. all did.
A follow to the revolutionary Super Mario 64, Sunshine brought Mario to the beautiful Delfino Island, the best hub world the series has seen including the best theme. Not just the hub, but the whole game was was decorated as a getaway paradise. Super Mario 64's Castle and the Galaxy games space theme were fine if standard, but Sunshine just eats their lunch in the personality department.
Super Mario Sunshine was the best 3D Mario title all the way up until Super Mario 3D World decided to be one of the best games since the turn of the century. And now it is even serving as inspiration for the highly anticipated Mario Odyssey.