Immortal Defense at its core is a tower defense game--a game of strategy where you place down defensive structures and seek to prevent enemies from reaching what you are protecting. In Immortal Defense, the enemies move along a set path and have to be destroyed
One unique aspect of Immortal Defense is that the mouse cursor itself fires at enemies, and can charge up and execute special attacks. - Game designer
The above quote pretty much explains what the game's about. Pretty neat eh?