Every Nintendo 64 owner remembers Mario Kart 64, and that game set the stage for multiple sequels across multiple home consoles and hand-held consoles. Mario Kart was a good game on the Super NES, but it was with Mario Kart 64 that the series really blossomed. But that game was not actually the best racing game on the Nintendo 64. That would be Diddy Kong Racing, which was released less than a year later.
Diddy Kong Racing (DKR) was a much bigger game, including a big over-world and a quest system similar to Super Mario 64. DKR also included boss battles against huge characters, who must be defeated one-on-one in a race. DKR also included planes and hovercrafts, significantly expanding the ways to race. There were also many secrets to discover and unlock.
My only problem was the requirement to finish first in every single course. Mario Kart 64 was much more forgiving with the points system, allowing the player to advance even if unable to finish first in a particular track. The roster itself was pretty unremarkable, with generic animal characters. The only recognizable character was Diddy Kong, though others would appear in games later on.
The power-ups were also much more generic than in Mario Kart, but unlike the first game the power-ups were not random but instead assigned to a specific color. The ability to collect more power-ups of the same kind to make them stronger also added to the game.
It is unfortunate that this series never did continue, with Nintendo investing more into the Mario Kart series. I see no reason why DKR and Mario Kart could not have existed side-by-side, but Rare becoming part of Microsoft ended the years-long cooperation with Nintendo.