The concept is fun and in the theme. At start I struggled a bit, crashing my car right into the cars that I just illuminated x)
The graphics and sounds are ok, although differents cars skins could be nice (even just colors) and some sfx for breaks, turns ...
For the game design, I think adding some kind of energy bar to make the player use his light wisely (with why not some battery on the ground in order to refill). Maybe different kind of lights, like a short one very effective but just around your car in opposition to a very ranged one but very tight (like shotgun and sniper) or it could be available as power up ^^
Could be nice for enforcing the race aspect to improve the sand/dust, I didn't feel a huge differents between the ground and sand.
I tried to details and give you some points as you asked ^^
Over that I liked the fact of having to concentrate over the race and at the same time to light up others cars to win, Good job =3
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In fact by all the points I gave, I think the diversity of cars is one of the lowest priority.
I think adding some mechanics would increase the lifetime for the game, giving to the player the chance of trying several strategy to win !
But it's already pretty fun, I put multiples points because you wanted to know where you could improve =P