Hard to decide! Super Metroid, Mario World, Majora's Mask... I can name quite a bit. But I think the one I keep coming back to is Metroid Prime, which just so happens to be my fave game ever. I guess just like Mario 64 and Ocarina of Time, it was a 2D franchise that transitioned beautifully to 3D.
A true sequel should improve and build upon its predecessor, but I feel Prime did so much more than that, considering how much of a transition going from 2D sidescroller to first-person action-adventure was.









