Basically, Banjo-Kazooie took all the elements that made Super Mario 64 great and improved upon them. BK does feel a lot like SM64 sometimes, but always in a good way. You can still do backflips, punch, and fly, but many new moves have been added, particularly aerial ones for our red-crested breegull companion. BK looks better, sounds better, and has way cooler worlds than SM64. This is truly a 3-D platform game.
The neatest features in Banjo-Kazooie are the transformations. The shaman Mumbo-Jumbo turns you into a variety of cool creatures, including an alligator, a honey bee and a ...pumpkin?! Neat! Each transformation allows you to perform specific tasks within the world, usually to get more Jiggies. The pumpkin even gets to take a little trip down the throne for a Jiggy. Now that's creative! (although more than a little disgusting) The only bad thing is that the transformations will only work in one specific world. For instance, you can be a gator in Bubblegloop Swamp, but not in Gobi's Valley. Shame, really. I would've liked to try being a pumpkin in other worlds.
Graphically, the game is a masterpiece. Rare is now famous for beautiful graphics, and they certainly live up to their reputation here. Banjo meets a wide variety of flora and fauna, each of which looks pretty realistic. Sound effects are good (the croaking frogs in Bubblegloop are great!), but I would've liked to have had real voice effects. The character "mumblings" are cute, but they get kind of old after awhile (especially Bottles the mole).
Aside from that, Banjo-Kazooie rocks the house. It may be your typical platform game fare, but that's part of the fun. There's a reason why platform games have endured since the early days of video games. BK adds a fresh new face to that wonderful gaming genre.