Great game, cool concept and fun gameplay!
My favorite levels were the custom-designed levels with fewer pieces. In all the "__ chess but you play as a tank" levels, there were too many enemies on screen for the game to feel strategic and it just felt like I was spamming in hopes of hitting the king. The first one was cool because that's the name of the game, but they overstayed their welcome.
Also, I wish the enemies all moved at once because it is really hard to predict when I need to move when they are staggered.
I think the tank control would be more satisfying if it slid against walls when it hit them diagonally rather than getting stuck on them, especially since there are so many one-tile corridors.
Overall, a very nicely polished game with a fun gameplay concept. Keep up development on this and I can see myself wasting a lot of time into it!