X-Morph: Defense is a challenging game. If you don't prepare your defenses well, then you simply might not be able to shoot your way out of a tough situation. Humans attack in really large numbers so you have to build a maze that will slow them down and give you time to destroy them. Fortunately we've got three difficulty levels so if the game is too hard you can switch to a lower difficulty setting even during a mission (which resets leaderboard score). Check out this video to see what happens if you don't prepare your defenses well.
https://youtu.be/27ahCxn1-e0