Well I don't know if it's the best N64 game, but it's defineately one of the best. I loved the game, and the fact that it was only about 15 hours long didn't even bother me since what was there was great.
And Chernobyl Hamster, have you even bothered looking at N64 games? It's far from being the first M rated N64 game, what about Perfect Dark, all the Turok games, and the 3 South Park games? And I know there are more, I just can't remember any of them right now.