I think you made this game too difficult.
You made one of the enemies appear too early into the game, or you made it too powerful.
Gray triangle like body, blue side things. Take a million hits to kill, destroys the base in two seconds. Usually one of the first 3 enemies to appear on all difficulties.
I want to give this a 5, but I'm almost ready to give it less. This is not a threat, nor a promise. This is just to let you know your game is currently broken.