Ten years ago, Super Tux Kart would have been a perfect substitute for Mario Kart 64. It looks and feels every bit the mid nineties PC games it wants to be. Which makes it so unfortunate that it is currently 2008.
With several well done and very creative tracks, a nice assortment of characters and power ups and challenges to complete, Super Tux Kart is the sort of game I would have paid money for back in the days when everyone but me owned a Nintendo 64. Now it simply looks outdated. And not outdated enough to be retro cool, either. Just old.
It has a lot of features that could make it a great game. There's support for up to four players, but no control pad support, so you and three of your friends could huddle around the keyboard and invade each other's personal space and interfere with each other's driving. Up to ten karts can be in a single race, at the cost of severe slowdown to gameplay.
When you get right down to it, Super Tux Kart is just another kart racer. If I didn't already have so many at my disposal, I might be more impressed with but, frankly, it does nothing to distinguish itself from the crowd.