A few additional features I added:
1- Speed normalization. When player stops holding speed-up/speed-down buttons, they will naturally slow down to the default speed over time.
2- Player can jump in the air up to 3 times in a row with added particles. This resets upon colliding with the ground.
3- Rotation uses rigidBody torque, which is a little smoother than what was provided in the class.
4- I added a non-trigger collider to the head. When the player lands on their head, they still die, but they actually sit on their head instead of falling through the ground beneath them.
Playable here: snow-boarder by justindstein
My github: https://github.com/justindstein/snow-boarder