Very nice game! I never expected I could be entertained by these kind of semi-idle upgrade games, but I am. And yours is yet another take on it. It looks nice, it play fluently, and the sounds design makes it very satisfying to keep playing. Nicely done!
Maybe one suggestion, although that might overcomplicate stuff, to have some sort of way to command your soldiers. To make part of them go left, part of them go right, or whatever, etc ... Dragging boxes around them, or do that by drawing a line over your soldiers towards where they should attack.