Cubetractor isn't about having that single, innovative concept to give it form. Rather, it's about having multiple, different mechanics layered upon each other, with the focus on making sure they work well in tandem to produce a unified, holistic gameplay dynamic.
On the basic level, in Cubetractor the player has no direct means to attack or shoot. You have to crush enemies indirectly, by pulling Cubes to crush them. But be careful, because the very same Cube can damage you too.
Layered on top of this is a reverse tower defence mechanic. It's a strategic and frantic tower attack -- you'll need to plan how you'll engage enemy installations, deciding on the right towers to build, and where to build them, all this while dodging enemy fire. The thing is, you cannot build towers directly. You build them indirectly, by pulling two cubes together so that they collide.