i found the earlier levels pretty uninteresting, though it could be because i've played way too many sokobans and the puzzle mechanics are pretty much exactly like every other sokoban
the hopping & lack of a smooth transition from tile to tile kind of necessitates an undo button because it makes it hard to tell when to stop moving and you often end up pushing the key onto a spike that's never safe to step on. it's also made worse by the restart animation being slightly too long.
overall the game kind of feels like a prototype, it ultimately doesn't really seem to get anywhere with its levels. but i can see what you were going for with the shadows, i just think the concept could be pulled off better