Very fun! I liked all of the levels and how the difficulty scaled between each one. A few things I want to say:
The hitboxes on the cars were very unforgiving. I think you should make it a bit more obvious to the player that they were hit because I often felt like I shouldn't have gotten hit when I did.
While you did have multiple little guys in the game, most of the time you just combine them together to get to a hole or past a car. I think you couldn't went further with the theme and made certain puzzles with them, like having one of them go up to press a button which will unlock a door for the other, or maybe you have to sacrifice one so the other can progress.
Adding a bit of audio can really make your game more immersive. Even just a simple jump or hit sound effect is enough. Audacity is a powerful free audio editor and it's easy to use, maybe check that out if you haven't already?
Anyway, I still think you did an amazing job with this game! It was very fun, so congrats!