Really cool game, the artstyle is amazing and the idea is simple but fun to play
I would add some kind off score (or hight) to show the furthest the player has reached.
This is also done partly by the changing background but I thin It would be cool.
Also I would add a button to cancle the jump, it can be frustrating if you messed up the timing and still has to take the jump.
Great work, I enjoyed it :)