Shoot 'em ups: shoot down anything that moves
The phrase "shoot 'em up" amuses me; it's like... a redneck declaration of violent intent. As a subgenre of shooter video games, it's difficult to define. Shoot' em ups are usually identified with some kind of vehicle shooting down (pew! pew!) aliens, soldiers, planes, etc.
With this update, I bring you a few semi-unknown shooters. Dalek Attack is perhaps the only one you could possibly know (it's based on Dr. Who after all).