The only thing I'd change is the direction change...it's awful ;)

The track variations really reduce the boring-factor IMO. Maybe I shouldn't make it onbeat, but rather let it switch every time it completes one/two/n round(s). Because of the way the camera rotation is calculated it also looks incorrect on the actual on-beat frame. Maybe I could add a very short fade out to prevent this.

I dunno if this is possible, but you could add a twisting feature to the end of the track sort of like a mobius strip. Or just have the camera rotate around the track when you switch sides. For switching directions, you could simply turn the camera...it'd be great if you could slow it down temporarily, but you say it'd be uglified :( Possibly just move the camera back a bit after you turn it, not depending on the track, then push it forward afterward?
Also, how about a direction reverse without turning around?

A mobius-strip arrangement would be weird: when the camera is upside down, the track needs to bank in the opposite direction. And having the camera freeze and rotate would require the code to be a lot more complex. Remember that the camera angles are calculated in a very weird way (only way to make it go fast) and that I'm close to running out variables.
On top of that, actually making the track twist 180° or 360° isn't possible. To do this, I would need to implement code to rotate the 2 rails around the 'spine' at an arbitrary angle. This would mean a *lot* more multiplications and sines/cosines per point. I avoided this by pushing the rails up and down, and then normalising the offset. This allows it to rotate between -90° and 90°, but not over.

Can anyone explain why I can see rollercoaster v2 perfectly well, but Neon Coaster doesn't work at all?

- Krash

UC: I flipped the minus sign to a plus and increased the 6000 in the by= to ~50k-100k and I noticed that the track twists often, like (wait for it) a mobius strip. Oh yeah, the rollercoaster became pretty funky. :)

Yeah sure you can make it twist a lot, but I think Atero meant to include the one-sided property of a mobius strip: after one round, the track flips around and you travel on the other side... at the end it flips back again.