Super creative take on the theme. The artwork is super good as well, and I really enjoy that you get out of the way of the player and just let them figure it out. With that said, maybe a few more hints wouldv'e been nice, such as a cost display on the unit buttons. Also, the game could've used a little more 'juice' to put it into the next level, but otherwise I really enjoyed it. Good job!
P.S., I initially thought the red dots were spots you HAD to draw your loop through, and that made for some pretty interesting shapes that alleviated the boring solution of just binding it tight around your castle. Maybe worth thinking about.