Well, shit. This is the game that has been universally held as one of the (if not THE) greatest games of all time. What more needs to be said?
It's Mario, but in 3D. Yeah thats not a big deal nowadays but remember when this game came out it was the first of it's kind. There were other 3D platforming games before this one (Jumping Flash and Pandemonium on the PS1 come to mind) But nothing like this, a 3-dimensional, third person platformer with a free roaming, positionable camera was unheard of. And not only did they pull it off, they made a game by which nearly all games after it were measured.
First thing you notice is that Mario's controls are dead on accurate. Yeah you gotta hold the N64 controller in at that weird angle but it becomes pretty natural eventually. Lightly move the analog stick and he slowly walks, press it harder and he runs, do back flips, wall jumps, triple jumps, swim, punch things, bootie-stomp, all of it comes off exactly with no wackiness in the controls whatsoever. Just running around in the castle, climbing on trees and exploring is pretty fun.
The game is presented via Princess Peaches' castle, which acts as a hub to other areas (most of which are accessed through a painting on a wall somewhere.) Each level has a theme, forest, lava, desert, ice, etc, and each one has several missions to complete in order to collect a sufficient amount of Starmen to advance to the next area. Although the levels present you with one mission at a time there's nothing to stop you from doing them out of order (when possible.) Each level also has several hidden stars, and there are more hidden in various hidden places about the castle, for a grand total of 121 Starmen to collect, although only 70 are needed to complete the game.
The levels themselves show the usual Myamoto genius, each is pretty challenging without being too hard, do a good job of showing what needs to be done to advance without leading you by the nose, and each is packed full of secrets, shortcuts, and hidden areas. Some have you climbing hand-over-hand on fences, running on spinning gears while avoiding exploding bombs in the clouds, flying with a winged hat to collect red coins, shooting yourself out of cannons, climbing pyramids though quicksand, each one perfectly balanced and executed marvelously.
If I had a complaint with the game (which I don't, they're more like minor grievances) it's that boss battles are few and far between, and when you do have them they are pretty easy. Most of them involve you running around a character that is larger than you (a big walking thwomp or Boss bomb-omb for instance) and either butt-stomping it or picking it up and throwing it somehow. None of them are very hard, although the final battle with Bowser can get pretty hairy. The only other thing that can get slightly annoying is the camera, which has a tendency to wander off. But it's easily repositionable and doesn't get stuck behind or inside of things too much. For the first ever free roaming 3D camera they did a pretty good job.
A truly excellent game, a game which approaches masterpiece status.