The strategy I used for level 3 nightmare was to spam the weakest turrets, with a freeze lazer behind them. Regular defenses wont work versus aliens, they will rush your turrets before they can be killed unless you use freezers to slow them down.
Get rid of every single god dam enemies that can use stun stomp or any stun ability. Ive noticed that once you get hit, they tend to spam that same attack over and over again, which can screw you over majorly.
It was 4.10 with almost 80,000 plays and 8,000 ratings when it received a badge!