Pretty fun concept, but there's definitely some balance issues.
I found more often than not, my units would get stuck on a corner, then an enemy's bullet would snipe 2 of them at once, which made rounds snowball into impossibility. I also encountered a bug where the game was permanently in the Preparation phase and would softlock after I sent out units.
It's a great start though! Hope for the best if you decide to expand on this!