OK, I love NSR, but I am not quite so sure about some of the tracks - specifically the "Aerobatic" ones.
The loops seem pretty pointless - they don't add much to the game. I think if you are going to do stuff like that you need things like corkscrews,split loops (Loops with a gap that has to be jumped), crossover jumps - stuff like that. At the moment, "Aerobatic" is a poor name as no aerobatics are done (You are on the ground in a loop, not the air).
I suppose the problem here is that you end the game on an off-track, which could be an issue with some of these features.
Also, whilst I enjoy most of the Jump and Supercross tracks, I feel that there could be a bit more emphasis on gauging jumps right. Personally, I race boardercross (On a mountainboard, sort of like a snowboard, but with wheels, on dirt, downhill, and brakes are banned...) and some sections of some tracks I really like - bits where you have to judge a set of doubles just right or you are smacking into the face of the next set...
I would love to see more of this kind of stuff - and try and reward hitting that landing perfectly not just with reduced damage but increased speed. One idea I had would be to make some of the jumps have a proper transition on the landing rather than the table-top style most seem to be at the moment. If you had a transition on the landing and you hit it just right (And your physics engine worked properly) you would get a boost as you converted vertical speed into forward speed.
Another idea would be to put boost tiles on the floor at the top of the landing that make you go faster if you land on them.
Anyway, just some suggestions - keep up the good work.