The idea may look simple but the good level design and the sound/visuals keep you engaged. Good job!
Also, I think that the learning curve should be less steep, with a couple more “easy” levels in the beginning to make sure people get it. Also, I would change the movement to a tile-based system or make the collisions with walls less restrictive. Sometimes the difficulty of game came from that when you already knew how tot solve the puzzle.
Cool game :)