Very cool concept ! I like the simple micromachines like handling and the chaos that happens since the race is more of a checkpoint rush in an arena rather than laps around a track this captures the derby vibe very well. The music is also very catchy, but the best part to me are the car designs, they have that same insane carma look and humor to them :D
Only issue i had was the camara angle that sometimes hid the car behind the backgound, other than that no real problemswhen i tried it.
Overall, cool stuff ! Now all it needs is more arenas and cars :P