All time lowest price for this game on the MS Store.
From the website:
Unique fusion of a top down shooter and tower defense strategy. You are the X-Morph - an alien species that invades Earth to harvest its resources. Strategize in the build mode by carefully selecting various types of alien towers or throw yourself right into the battle. Build mazes for incoming enemies in an environment that provides exceptional planning freedom. Tear down buildings and collapse bridges to support your defense or to simply indulge in a spectacle of unprecedented destruction.