I really can't emphasize enough how great the minimalist visuals are. It's really satisfying to watch the battle unfold and all the mechanics and strategy elements are pretty slick.
I hit a little bug where all I had left was an archer against an enemy trebuchet and it kept firing on the archer but the archer never died. A persistent retry button would be a nice addition, so you might not have to close all the way out in the event of something like that. Or when I realize that I've made boneheaded unit placements (but honestly it's so fun to watch the battles play out I don't mind).
Really great work!