Featuring 20 towers, 20 types of enemies and 16 missions, this is one of the best sci-fi tower defense games that you will thoroughly enjoy playing. Your main objective during the game play is to defend your base from the alien attacks carrying out researches, unlocking and building defensive units. Your deployed units will be attacking the aliens that come in the range. You will be earning money for killing the enemies. This money should be used to make useful purchases that make your side more competent against the enemies. In order to be successful during the game play, you must use your strategies very effectively.