Just gave it a go - took me just over 15 mins.
Overall I would say it was pretty good
I liked the jump into the airport - not so keen on the jump out. In a T20 you end up on the higher road section, and although there is a ramp up there you can use to jump back down to the lower section, you are very unlikely to make it directly, so you have to reverse and line up to it. So it penalises you for going over the initial ramp too quickly - even though there is no indication that there is the chance for that penalty.
The jump later on over the canyon river is perfectly sized - and with the amount of room you have for a run up it lands you perfectly on the other side, which is cool. I lost time because I missed it originally, so reversed back to go over it. But I should have just continued and driven over the bridge, as you can reach the next checkpoint that way also. I would say if you have a jump there, then force people to have to make the jump.
Some more general points - on some of the early turns around the city, the checkpoints are put in the middle of the corner. I personally would put them before the corner, so that people can then take the corner how they see best. Also, if it is a right hand turn, for example, then most people would try and hit the apex of the corner. However many of the checkpoints are put too far out from the apex, so you have to treat each corner as a strict 90 degree turn - if you try and hit the apex you end up missing the corner. So it doesn't lend itself to people trying to get a fast time.
I would also stick to having the checkpoints on the right hand side of the road - some are, but a lot are on the left of the road. If you do the race without any traffic, then it doesn't really make a difference - although I think it feels strange to drive on the wrong side of the road for some sections - but that's probably just me. But if people wanted to add traffic to the race, then they would be forced to drive through oncoming traffic for a number of the checkpoints. No harm in adding that if that is what you are looking to achieve, but it felt random as to which side of the road you would be driving on. I imagine being forced to drive through traffic would be pretty frustrating...
Final point would be around checkpoint 27/28. I followed the route I thought you were supposed to take, but the 'Wrong Way' message came up. I re-spawned, and saw that you had blocked off other routes with boxes. I saw where the next checkpoint was, so tried to go the way I had been going. I got the same message again, carried on driving and then the road curved around and led me to the checkpoint. So the route was fine - it was just the game thinking you were going wrong. But you only learn this after you have re-spawned - which is annoying. You could add a checkpoint in-between 27/28 and that would eliminate the issue.
Just my quick thoughts - I have no idea if you were looking for any feedback - it's in no way meant to be a criticism. Just recreating the race we did last night took me a long time - so I know that it takes longer than it appears!!
I want to try and create my own race. I created an air race that I think is very good - although obviously no one really plays air races! But the creator tool is actually very good and easy to use. For me, the beauty of the track we did last night was that it stripped everything away and was just purely racing - no jumps, no crazy turns etc.