Too much text. Ten chapters in I co pletely stopped giving a damn about the story and just skipped all the dialouge. I came here to play a platformer, not read a novel.
I know you've said you don't want to add any new gameplay features to the game, but how about making a sequel? It can be based on the same model, but have much broader gameplay (campaign-ish stuff, upgrades, new items to throw at the cars, different cars (lorrys would be fun), and proper objectives. Just a suggestion ;)