Maybe allow for a free camera, to see where your units are. Or if you want to keep the focus on the enemy, maybe would be better to have an "arrow" at the edge of the screen pointing at your units, for each unit you have outside of the viewport (and then if you have too many, you can group them or smt). At first, I had the feeling my units died, as I was unable to see them, and they were moving slowly.
Another feature would be upgrades. This being a rougelite, maybe between each round, it would be cool to upgrade the units somehow, and also the enemy to have some diversity in stats/mechanics