Content review for this game:
Pertaining to content listed in the upper left corner of this site.
"E" for everyone: The story (like most Super Mario games) involves Mario trying to save the Princess Peach from Bowser, who (this time) has kidnapped her and locked her up in her own castle. This title was released in 1996, and was the first fully 3D Mario game. Thus, the graphics are going to be outdated, and, of course, Mario games in general have never been very violent, and this one is no exception. The very worst it gets is when Mario jumps on an oversized, walking mushroom's head, which results in it flattening like a pancake, and then disappearing in a small puff of white smoke. In other words, there's nothing to worry about, very mild stuff.
Content-wise: When this game first came out many kids 6- would have probably wanted to play this game. Now that Super Mario Sunshine and Super Mario Galaxy have been released, if kids this age are into Mario, they'll probably want one of the two above. And this is good, because although they could maybe run around Super Mario 64's main hub (in the form of a castle), there is really no way they could complete even the first level in this game. Get them a later one in the series.
Difficulty-wise: The game starts you out by placing you in the main hub, which is in the form of the fully explorable Princess Peach's castle. The castle's many doors lead to portraits that act as portals to the game's levels. When you jump through a portrait, a white screen comes up and shows six empty stars representing 1 of the 120 stars in total. Each of these six stars represent a certain objective, and once you complete this objective, you'll get the star, which will start to unlock more doors to more portals and levels, and ultimately lead you to the final showdown with Bowser himself. Each of these levels also have a seventh hidden star, which is unlocked if you collect 100 coins in a specific level.
Mario has many moves at his disposal, and can jump, double jump, triple jump, side jump, long jump, backflip, punch, dive/slide, climb, shimmy on poles/trees and more (button layout depends on if you're using the Classic controller or Gamecube pad). As you see, the controls are pretty complex, and the skill required to pull some of these moves off can be somewhat advanced. Even the first level starts out at a moderately high difficulty, and begins to gradually ramp up from there. Also, because this was the first 3D Mario game, compared to today's games, the controls and camera are heavily outdated (especially concerning kids). An example are the flighty controls while jumping from small platform to platform. When you stop moving Mario, sometimes he'll move just a little bit more afterwards, causing more inexperienced players (younger kids) to fall to their doom. The camera is also troublesome, as the automatic angles sometimes give you a bad view of a tight situation, and the manual camera is often too touchy (and clumsy) to control.
So, difficulty-wise, I could see some very dedicated (and patient) kids 7+ maybe make it through the first few levels (maybe). But, other than this, the problems listed above, and the fact that the presentation is so outdated, I don't think this age group would enjoy it anyway. However, kids 10+ that are interested in this game could complete a good chunk of it, and are probably skilled enough to compensate for the camera and control problems.
Fun for: Kids of many ages could have fun with, and play elements of this game, and older age groups could complete a good chunk of the game. But, overall this game does skew more towards adults (only a bit), and I could see them only complete it in its entirety, find all the secrets, all while having the most fun the whole way through, especially since most of the adults who are going to buy this remember when it came out (in other words, nostalgia).
Closing comment: This is the game that started the 3D Super Mario series. For its age, it is extremely polished, deep, and challenging (I've only completed about 3/4 myself). Difficulty-wise, I could easily see kids 10+ play the majority of it (if they're interested in the first place). But, because of the overall difficulty this game presents, and because of the outdated controls and hard to control camera, I think kids 7+ are better off playing Super Mario Galaxy. So, I recommend this game for ages 10+.