Fun, decent level design, but the game is sorely held back by the platforming physics. I would get caught on weird ledges, or the character wouldn't jump for some reason (I was using Rad). I tried another playthrough with the Banana Car, but the physics issues only increased with the high speed. The coins feel like they also have collision, which is odd. I would give this more time, but I I only made to the second level (on both characters) before receiving a game over. The menu music is also a little annoying, but that's just my opinion; others may think it's fine. On a positive note, the UI and story sections are really well made. They look and feel great. Also, the AI opponent is fairly advanced, jumping between platforms and collecting coins instead of just sliding across the backdrop (like I have seen with some other games).
All in all, this demo has great potential, but it's good level design and concept is overshadowed by suboptimal physics. I still look forward to a completed game.