Oof, that was stressful. But in a good way. I was not able to beat last level, but I can see it is totally possible with a good strategy.
One thing regarding controls: Having Q for getting back to the map selection is dangerous when you are using WASD for camera movement in game. I hit Q accidentally several times during playing.
Also adding some basic sound effects always liven game up. Without them it feels a little "empty".
Its a nice game you have there!