Yeah I spent a lot of time polishing the game and improving the pathfinding, as I had quite some difficulty coming up with interesting puzzles. Maybe you noticed the towers returning to a perpendicular angle, if there were no targets. Or how they aim ahead of enemies to account for the movement of the enemies. ;-)
The connection to the theme is the twist on typical tower defence games (puzzle game instead of strategy game). I have to admit that the connection isn't as great as I would have liked. I'm glad to hear that the difficulty curve is on point.