Incoming/Incoming Forces.
Incoming, because it's probably THE cheesiest sci-fi shooting game. (A combo of UFOs, secret government tracking facilities, moonbase attacks with NASA vehicles retrofitted with guns, and duels through giant space portals with experimental new vehicles. Plus you can play as a turret, tank, copter, fighter, alien ship, hovercraft, etc.)
Incoming Forces, because while the storyline wasn't particularly motivating, the visuals were good and the music kicks ass.
There's another game I'm forgetting but, uh, I'm forgetting what it's called right now.
