Gaia Defense is a tactical defense/strategy game. Aliens will attack your defenses on their weakest point, or get around them and even dig their way underground... The battlefield might change a lot before the level is complete !
Luckily, you have 16 different units to build to help you defend the Bomb. Turrets, walls, generators... Be very careful where do you build them, their placement is critical to win.
Play through the 19 campaign levels and 10 survival levels (with leaderboards), then use the level editor to create and share your own levels, and try the other players' creations. The game includes a level ranking to help finding the best level creations.