I love the concept of a "reverse tower-defense" that's like a puzzle game where you're trying to place units in the right orders and spots to get through the defenses.
However, I found both the puzzle and arcade modes confusing at times. For example, I didn't even realize some units could damage towers until I did it by accident while trying to figure out the second level. And some units seemed to attack in ways that I didn't totally understand. In the arcade mode, I found the movement of the towers completely unpredictable and just tried to time things to get through.
All that said, this is still quite impressive and fun once I got the hang of all the mechanics at play. I think it would be a concept worth exploring further if that's something you're interested in doing. Oh, and the art is absolutely adorable. Great work!