This is such a cool demo; it's simple, but every aspect that is there feels well thought-out. I'm very impressed with how you did the pathfinding, especially the fact that it even contributes to the ui by showing you all the available squares (and the fact that enemies can block the path of other enemies and cause them to reroute).
Great work, and I'm hoping you can add some more troop / level variety, as that could make this even better.