4. Strike Force (1991) Speaking of clones, Strike Force was the second sequel to Defender, essentially improving upon the side-scrolling shooter in every way. Once again, you find yourself piloting a space ship low over the ground of an alien planet, rescuing human colonists from the hostile alien forces. The aliens are pretty badass, with their ability to mutate the humans into enemies and commandeer stray vehicles dotting the plains to use against you. But there's an ace up your sleeve: probably the first example of friendly AI that wasn't completely useless in the form of your loyal squadron of commandos. You could drop them to the planet's surface, where they would provide cover fire, rescue colonists, and sometimes kick ass independently of you, jetpacking around and shooting enemies until either killed or summoned by you. Until deployed, the commandos would hang from the belly of your spacecraft like heavily-armed remoras, and it didn't take long before you became protective of the little buggers, seeking angry revenge whenever the alien forces managed to kill one. Defender was well-known for being an incredibly fast-paced and intense game, and Strike Force managed to up the ante significantly.