The tower defense genre has a large spectrum of flavors and a rich history on the mobile platform. The games are simple to pick up, addictive to play, and each has its own take on the genre. Sentinel 2 picks up after the destruction of Mars' colonies by the invading alien hordes. Now you are tasked with the defense of Earth's facilities. To aid you in this endeavor, you have a full range of defenses. Simple machine gun defenses, bomb throwers, slow towers, sniper towers, and many others can be upgraded and used to turn back the hordes of cookie-cutter aliens.

You earn cash by defeating the various waves of aliens or by hiring drones to gather resources for you. The resource-gathering aspect of the game is small, but integral for later stages. You can recruit drones to gather funds for you, repair your base, and eventually, help recharge your special Sentinel powers.

The Sentinel powers are arguably the most original aspect of the game, and are reminiscent of bonus powers or super weapons from real-time strategy games like . When the hordes become too much, you can deploy one of four Sentinel powers that will aid you in combat. These include missile bombardments, an orbital canon, attack drones, and a glowing yellow eye that slows down your enemies in a wide area. They are recharged over time, but hiring drones to help with the process ensures they'll be ready for redeployment faster.

In addition to standard assault mode, Sentinel 2 offers an endurance mode and special challenge missions. The endurance mode basically tasks you with surviving as long as possible against a never-ending series of attacking waves, but the challenge missions are more creative. Each mission tasks you with a special limitation on your abilities and thus enables for some creative strategizing. One mission requires you to take down a huge enemy unit with only limited resources while another has you taking out enemy forces using only Sentinel Powers.

Origin 8 has a partnership with , ensuring that you can share your top scores with your fellow players while introducing some social capabilities to what is primarily a single player game.