Good work! The art and animation work really well, and the physics/movement are quite cool.
However it's really hard from the very start, I actually tried the game a couple of weeks ago and couldn't even get out of the sewers section. Today I tried again, and with some practice it finally "clicked" and I was able to control the Jook more precisely, and reach the second, and later the third area.
But even then it's way too unforgiving, as hitting a wall in section 3 can still send you all the way to the bottom... doors help but only part of the way, there are still some frustrating sections to pass like the first blade of grass barring your way after the sewers.
So all in all the learning curve is too high (gave up the first time without passing first section) and even if you persevere it's too unforgiving, and thus frustrating (and I do love some difficult games like VVVVVV or Super Hexagon).
All that being said, I see a lot of potential with some more difficulty balancing. The collisions can be made more forgiving (factor in speed further so that low speed collisions don't kill you), and the level designs can be improved to be more forgiving too (no impossibly narrow sections when you need to be near-static to be able to pass and hope that the near-static collisions won't make you lose, and no falling to the very bottom - at most you should fall to the previous biome/level). The game could also better convey how the different elements work (first time I played I didn't understand what the door was, and how the checkpoint flags work - when I did manage to reach the first flag, then died and walked to the right all the way back to the beginning, that was quite frustrating).
I loved the intro scenes, the animation work is really nice :)