Thanks for your feedback!
I will consider these issues and make some conclusions.
About checkpoints and keycards: I tried to put the keycards in such a way that they would be as close to the next checkpoint as possible, but seems like I made a slight mistake with that, I guess ;-;
Also I tried to don't make checkpoints too often cuz that will make game too easy.
About "land on one foot on the ledge": I could make something else instead of that, sure. That's really sucks. Seems like I didn't have enough creativity for that.
About indication: I tried to make it notable with this "?" sign. If you come closer - you'll get killed. Maybe I should've changed distance for it's to show up.
Hope you enjoyed rest of the game and thanks for your appreciation of the graphics and music!