Someone else mentioned it but I also agree that using middle mouse button is an interesting choice, the only way I was able to figure that out was by reading the description so not very intuitive. Hopefully you can flesh out the game with more levels and obstacles cause I definitely see the potential!
I think this game would work very well as a 2-player game. Have one player choose an escape path and the other place obstacles then run the simulation of whether or not the prisoner escaped. Then its a game of psychology, trying to get into the mind of what your opponent and how they would escape/setup.