It's Missile Command 2.0! Not really, but kinda!
First Contact takes the simple gameplay of Missile Command and translates it into a good 3D game engine. The goal is simple: defend the bases on Mars against constant alien attacks. You do this by rotating around the planet and zooming in and out to tap objects that are flying towards the surface. This consists of missiles, UFOs, and other alien devices. When you tap the incoming threats, missiles are launched from the bases on the surface of Mars to destroy them.