Let's get this out of the way: Mario Kart 64 was, and still is, the best kart racing game ever.
Mario Kart 64 set the standard for the series when it was released in 1997. In many ways a more fully realized version of Super Mario Kart for the SNES, this was the first Mario Kart to feature true 3D environments, and had players flying off ramps and bouncing over rolling hills. The track assortment in this game is hands-down the best in the series. From Toad's Turnpike to Wario Stadium, MK64 featured unique, fun tracks with memorable gameplay innovations.
Recent games in the series seem sluggish compared to this game; Mario Kart 64 features in-your-face action and racing at breakneck speeds. The items are more potent in this game than in later games; bulls-eying your opponent with a green shell just hasn't been as satisfying in games since this one. The power sliding technique, first featured in this game, has been dumbed down recently, as well. In Double Dash!! and Mario Kart DS it's possible to power slide through every inch of a course, and it's nice to return to a game where power sliding involved actually drifting through a turn like it was intended.
Graphically MK64 looks dated today, but it's not hard to remember why these graphics were once thought of as gorgeous. Environments are bright and colorful and each track has its distinct appearance. The music in Mario Kart has suffered in recent years, especially the drab soundtrack in Mario Kart DS. The tunes in MK64, on the other hand, are all memorable and appealing, which makes me wonder why Ninendo doesn't recycle some of these classic tunes like they have in almost all of their other franchises. MK64 also gave the characters voices, many for the first time, and it's still fun to hear their quips as they race.
MK64 was the first to offer 4-player multiplayer, and it's still a blast to play today. Races are intense and highly competitive. Battle mode, however, is the one area that has been surpassed in recent games; the battle arenas in MK64 are sparse and too large for only four combatants, and the only available mode is the standard Balloon Battle.
If you've played Mario Kart 64 today, you'll instantly remember why you loved it ten years ago. If you've never played it before, it's only ten dollars on the Wii's Virtual Console, and for those ten dollar's you'll get a better kart racer than any available today.