This is a great game BUT ITS WAY TO HARD. nightmare? More like utterly impossible. 3 stars ? NOT POSSIBLE. 5 electric zombies while i can only put out at most 3-4 units and all get killed instantly. zombies are way to overpowered to the point it isnt fun at all. Oh upgrade your units yea i tried but it doesnt matter they still die FAST compared to zombies. Map 3 level 58 amd chsllenge 1 are TO HARD. Map 3 is filled with hard missions. Zombies are to strong. To many electric/ regular zombies.