(N64) Mario Kart 64

Mario Kart 64 was the first title in the series to use 3D polygon graphics which allowed new features such as elevation, bridges and walls not available with 2D graphic and Mode 7.
There are still 8 characters selectable but Koopa Troopa and Donkey Kong Jr. were replaced by Wario and Donkey Kong respectively and other new addition were the infamous Blue Shell and slipstreaming.
The presence of 4 controllers made Mario Kart 64 much more multiplayer oriented than Mario Kart becoming one of the main feature of this series.