I think art-wise you could've restricted your palette a bit more. Some assets have a lot of very similar shades which could've been simplified to a smaller palette. I think you could also look into pillow shading and study how to avoid it.
I appreciate that you have a uniform pixel scale in the game world, all assets blend well and the art style is cohesive.
You have a mechanic where you can shift gears, but as of now, it seems like there is no drawback to going at max gear all the time. A way you could've made the shifting mechanic more engaging is that you could've added a trade-off to the higher speeds in the higher gear by making higher gears turn slower. This would force players to weigh in pros and cons and constantly shift up and down to optimize their driving. Go fast in straight lines and shift down to turn in corners and back again.
The Dice mechanic is not much more than a UI replacement for random numbers, the theme could've been more deeply ingrained into the game design.
There doesn't seem to be much of a difficulty ramp up. I would tweak things so each delivery would require faster and faster deliveries until players eventually fail and then prompt the player with their high score before ending the game!