To continue my previous comment, I'd love a implementation of secret areas or something. I kept on figuring out to save a bunch of boxes, but it's pointless. But you could have stars or something where you need to save all boxes. Like from the game blocks that matter. This could also work for a sequel.
I really liked the overall game, and I think it was well balanced. My only problem is the star system. The controls are a bit slippery jumping, and I kept on making it to the end of the level, and barely missing a jump at the end. I'd say change the way stars or given, make it more forgiving, or remove it entirely.
One problem is odd hit detection for some platforms. In the sky world in the lower left, the platforming is impossible because when I land on the edge, half on, half off, it teleports me a smidgen off the platform, because it thought I didn't land.
Bug: on the 2nd level, the desert, i was fighting a wolf boss that kept on teleport to me, and attacking, but on the 3rd time I was near the wall, and it fell out of the map, leaving me stuck with 5 keys.
Quick Note: The armor plating upgrade says: INCREASE the amount of damage you can take from colliding with other cars and SUV shields. THe "increase" should be "decrease".
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OH NO.. okay, will look into it.