Super cute! I loved the different levels and their environments. I love the idea of switching cars, super creative and fits the theme perfectly! However, I often found there wasn't a lot of reason to switch cars. I would either get too far ahead/behind that I wouldn't be near any cars(that's probably just an issue with my skills lol) but the main thing that stopped me from wanting to switch is that it did throw me off when switching cars and I would spin out or go off the track immediately after switching.
I also do really like the idea of a physics racer; when I usually think of racing games I think of Mario Kart and Crash Team and while they're fun in their own ways, they're not really physics-based so I totally dig the concept of a physics racer!
Great job! :)