Graphically nice and clean, but damn hard
Well, you warned us... the regular levels are really not easy. In fact, the tutorial levels aren't easy, but they're not nearly as difficult as the regular ones. A few comments:
1) Seems weird that you can beat a level and still feel like you "lost" because you didn't have enough juice to get to Bronze. If the goal is to get there with 100 mL, why not just start the person with 100 mL less than you do now and make the goal just to get there at all? Alternately, make 0-100 mL the new Bronze, and change the other medals to Silver, Gold and Platinum. Hard is one thing, but throw your players a bone now and then, eh?
2) Likewise, since dying without having collected an orange resets your juice meter, why not have each orange save the amount of juice you had when you collected it, and allow you to continue from that point with that amount of juice (maybe minus ten or something each time) instead of what you died with? It'd make it a little easier to get through the levels at least.
3) For the next version of the game, maybe allow people to save their replays and then play against their own "ghost line" the same way many car racing games allow you to see the "ghost car" representing your best race to date. Normal folks are never going to be able to compete with the global high scores, so being able to race against yourself would be fun.