Nice twist playing levels backwards. Great work recording the lines! For the most part the controls felt good and the visuals were easy to understand except the start point of the level.
One issue I had was finding the playable square on new maps at first glance. Maybe adding some visual indication for a second on the player when the level starts could help. Also disabling players input for one second after losing a life isn't a bad idea as I sometimes would respawn adding some direction and jump inputs causing a 2nd life lost.
On my first play, when I arrived on the second level, 9, I rushed to the spikes thinking that was how the game was meant to be played. Only then that I understood you needed to reach the door before dying.
Another issue was with the wall jumps. It seemed like I could only do wall jumps with a face on the wall. If it was an edge the wall jump was inconsistent. This made the level design feel weird. Although the levels were interesting, requiring skill and intimidating as they were to be the last levels, they felt unfair as they relied on inconsistent mechanic. That could be just me being bad at the game.