One of the best platformer's of all time.
The gameplay itself was simple: solid enough for previous fans to be satisfied with the new 3D experience, yet at the same time accessible enough for newcomers to approach it with ease as well. The storyline itself was uninteresting and consisted of the basic "rescue Peach from Bowser" plot, though the game was never meant to be story-heavy at all to begin with, so that wasn't a problem. The main goal of the game was to collect stars from a total of fifteen different levels, gradually progressing throughout the castle and unlocking new places to explore in. A level was indicated usually by a portrait, in which Mario could then jump into and explore. There were a total of seven stars in each level, each providing unique challenges, aside from a "collect the red coins challenge" and "collect one-hundred coins" (which were implemented in all levels of the game). When enough stars were collected, you may then proceed to one of Bowser's stages, where you would first journey through the area and then eventually fight face-to-face with him.
While it might not look like much now, Super Mario 64 looked outstanding for its time, creatively blending a visually appealing artistic style with exceptional graphical quality. The soundtrack was great as well, as it kept the original Mario theme that fans grew up with, but taking it to an entirely new, cinematic experience that drew players in even more. The camera was a bit to get adjusted to, especially for those not familiar with 3D gameplay, though it became easy enough in a short amount of time.
If, for some terrible reason, you were deprived of a childhood and didn't get the opportunity to play this fantastic game, I suggest you do whatever it takes to get your hands on it and enjoy. It's a memorable experience you won't forget.