Three war-scarred commanders are defending their properties — and the planet — from an alien force that wants an explosive mineral badly enough to kill everyone standing between them and it. Sentinels is a first-person tower defense hybrid in which automated turrets handle the bulk of the fighting while you join the action directly with grenade launchers, lockon missiles, and machine guns. Customizable mods — force, phasing, armor piercing — let you build a preferred loadout as you face four alien commanders, each with their own tactics and buffs.