Great concept, and perfect delivery on the game jam theme. I love you you could still see the little guys working as you go through the level.
My only piece of constructive feedback would be that the bullets came out fast enough when I had one guy on each type that I never needed to focus them on building a specific type. Maybe there could have been larger clusters of enemies of a specific type, or perhaps two specific types, and lower the bullet production rate? Or maybe lower how many you can keep stocked of different types.