Easily the best platformer on the Nintendo 64, if not the best platformer in existence.
Speaking of difficulty, I do admit that this game can get very frustrating at several points and is much more difficult to beat than Super Mario 64. The game does often require you to think outside of the box.
Another great thing about this game is the wide-open areas built purely for you to explore. Although many of the worlds are somewhat stereotypical for platformers (with the generic Ice, Water, and Desert stage), the game is filled with secrets for you to find.
The controls for this game are very easy to work with and will never really give you any problems as well. Along with this, the game also constantly provides many more techniques for your advantage.
With a balanced difficulty, massive environments, and easy to master controls, this is a great game and easily in my top 5 favorite games of all time. I would recommend any N64 owner to pick this up if you get the chance.