This game had some pretty fun puzzles, and I found the game enjoyable overall. I agree with another reviewer that the character movement was a bit off and personally too fast. I'm also not sure if it was due to when I activated the ghost or what, but there were a few times when the ghost would hover over the button by a few pixels rather than directly on top of the button. For most levels, this wasn't a problem, but there were some (namely the ones where gates needed to be changed from one to the other) where this was problematic and required a restart.
The backspace restart was a poor key-binding in my opinion. While you do note the mapping in the first level, I didn't need it until much later. When I needed to manually restart, I pressed the enter key repeatedly. (I got the symbol confused.) It might be worth also mapping the R-key to restart, as this is a common choice in puzzle games with levels that might require a manual reset if the player makes an error.
I played the game without sound on my first run-through, but I don't feel like I missed much. The music was okay and seemed to fit the visual aesthetic, but I would have been nice to have some additional sound effects in the game, such as when switches were activated, when the character jumps, or when they beat/fail a level. Just something that gives the player some auditory feedback would be a welcome addition.