I like the concept, and your take on the theme is great and very innovative, but it gets boring pretty quickly since there's no way to get much further than the farthest. Visuals are great, though the cacti could have looked better. A more dedicated main menu would have been preferred.
For the sounds, the car sounds great, but I would also have liked some more sound FX for, for example, when the car stops or when you set a new high score. Some music, or ambient sounds/music would have enhanced my experience further.