I like tracks that require you to use the curbing, at least some of them. I find those more exciting to drive. There’s a lot of ways to do this wrong, though, and then you end up getting nearly thrown out of the kart. Those tracks with curbing like that aren’t so fun.
Another favorite feature I dig in tracks are places that make braking zones very tricky. For example, the “Sand box” corner at Adams Kart Track is notorious for being really, really hard to figure out. It required you to lock the brakes up, slide the kart sideways ever so slightly to the right, then release the brakes at just the right moment to get the kart to roll the other way into a sharp left hairpin. It was really fun to get right.
One of my favorite tracks to drive of all time has to be Grange (I’ve mentioned this before), because they managed to make the elevation change really tricky. For example, they made one corner a 180 degree hairpin, sloping downhill, off camber. It was the wildest thing. They also have a fast right hand kink at the bottom of a long downhill straight that heads into a hard right hand hairpin for the first turn, which made race starts really challenging.