Mostly played with the track editor so it's where I want to give some feedback. Basically, what it needs is a way to paint tracks via curves (similar to AI curves). Making a road is quite wonky with mouse, even with "rope length" (a.k.a. stabilization) so being able to set up a curve and then tell the game to paint certain texture along it would be wonderful.

Also, being able to switch the water to lava (instant death and respawn at the last checkpoint, in the middle of AI line) or quicksand (the car slowly sinks in and is possible to get out if you're quick enough, but if you're not and it sinks fully, see lava for what happens).