Wow, nice, and there are plenty of levels too!
The idea is really interesting and could give way to good puzzles!
Some random comments (but I still love the game):
I thought it odd that I destroyed all the black pieces and kept my king and knight, but it wasn't a victory. I had to get my knight killed for the level to complete.
At another point, I finished the level with one black knight still standing (on the left of the king).
The end goal should be clearer. I saw later than the goal was for the king to go right. Maybe the king should automatically go to the right position when all enemies are defeated, so the player can understand the goal more easily.
A lot of puzzles can be brute-forced. Maybe there should be more constraints on some movements, like towers must eat a black piece if they go toward it. Otherwise, it's so easy to manipulate them.
Some puzzles are way harder than others. The second one for instance really asks you to think more than others.