I am very impressed. I have been messing around with 3D in GMS and it is very confusing, makes it even more impressive you've built this.
I love how it feels to play this game and i am really happy that there are options like no npc collisions (i found that really annoying). I get real mario kart super circuit vibes from this one, even tho i haven't played that game. The game is extremely intense (in a good way) tho i feel like the road itself could be made a bit wider and added some collision to make the running of the road feel more natural. The music is top notch, really really love it :)
The one thing i am a bit iffy on is how you play trough the courses themselves. I don't like the fact that you can't continue onto the next course until you've gotten into the top 3. It is a real shame that i can't play all the courses. I think organizing them into smaller packets of levels that you play trough with some sort of way to unlock them would be awesome. That is a very mario kart way of doing it, but the current arcade mode really is not my cup of tea. Maybe you find some other interesting way of doing it, but i don't think the arcade solution would be the best for a full game with more courses.
But overall i really loved this game, an easy 5/5 rating on this page.
edit: i finally beat all the 3 levels and it makes a bit more sense now.