Happy to be your 20th rater! :) I really liked this game, it was really fun to play. You got the challenge curve right with the gradual introduction of game mechanics. The texts were also useful for finding the right flow through a level.
A suggestion to the keyboard controls. I saw that the arrow keys can be used for left and right movement, but not jumping. If you would add the up arrow button as a jumping option, it would be much more comfortable to use the arrows with the right hand and space with the left.