Sadly I wasn't able to finish the game because a checkpoint would leave me too much on the edge to get back on solid ground to jump correctly. But the game has SOOO much potential! I never actually seen a platformer in which you have to precisely coordinate jumps relatively to the ground the character is facing. Nothing more satisfying than aligning the top of the present with the ground and making the jump in the direction you want!
Maybe fewer slopes and more lenient ability to jump (open the box) would help making this game a little more fun and functional! Maybe having the possibility to always open the box to perform a jump can be a step in the right direction!