First : I really love that game, even if it's kind of long doing all the crazy missions... But I'm going to have it, I'll play my life :P!
Second : Don't lose your time getting THEL, buy missiles lauchner, pretty much better! When you have enough, you can delete them. But be sure having ebough missile launchers, or ring ship are going to destroy you!
Third : Reparing towers are NECESSITIES, NOT OPTIONS!!! It's really going to help you having them. And try having two of them, they repair themselves! By buying them, you make defend missions are pretty easier.
 "i saw her too, with lasers"){kind=icon}
 "Sola Rola - The Gravity Maze"){kind=icon}
 "3D Logic 2: Stronghold of Sage"){kind=icon}
 "This is the Only Level TOO"){kind=icon}
 "Doodle God 2"){kind=icon}
 "Bunny Invasion: Easter Special"){kind=icon}
 "Gibbets 3"){kind=icon}
 "The Soul Driver"){kind=icon}
 "Days of Monsters"){kind=icon}
 "Wish Upon a Star"){kind=icon}
 "Upgrade Complete 2"){kind=icon}
 "Elephant Quest"){kind=icon}
 "The Space Game: Missions"){kind=icon}