I had to see what all the fuss was about and MAN there should be fuss.. This game rocks my socks. I've been playing it all day.
However, it is only a demo and there are many glitches. If you hit a wall, you're stuck to it, and the Heavy characters take about a lap to reach full speed. Sometimes if you fall off the course, you plummet to your deat in an endless cycle.
But when playing, it's fun. The music is good, the characters look great, there's tons of secret characters---it's just grand. And it captured the semi 3D-ness of Mode 7-esque graphics. Splendid.