Shoot ‘em up games are normally games that involve spaceships flying around and shooting the shit out of anything that gets in its way. The enemies normally range from other ships, to creatures, to animals, to just balls.
Shoot ‘em ups have been popular as they were cheap and easy arcade games to produce by game companies. They are inherently sprite-based games and simple to build as they only require a few sprites and motion controls. Though the numerous amounts of them are amazing.
There are at least a hundred games that fall into the shoot ‘em up category. A very select few of them are
The differences between the games are usually based on the sprites of the games and the attacks. There is normally a control stick or control pad and two buttons. One button is almost always attack and the second button will either shoot as well, or select a special upgrade, or do a special attack. Each game is unique in the use of the second button.
The game's sprites do change to a great extent. Tiger Heli is a helicopter game where you shoot up buildings, where Galaga is where a ship shoots up space aliens. Centipede has a shooting gun that tries to kill Centipedes. Each game will usually use sprites that are unique to their game. In some games the stage moves down a corridor such as Tiger Heli and Gradius, while others like Galaga and Centipede are stationary installations.
Shoot ‘em ups tend not to have stories, but they are fun when you wish to just destroy other races. The games are usually just to shoot anything that you can see. The reasoning is usually because they are going to kill you. The games tend not to require thought but more likely to just use fast hand and eye coordination.
The shoot ‘em up games have faded to an extent when three-dimensional games started to gain popularity. The shoot ‘em ups are normally two-dimensional games. There are remnants of them in some games but only a few shoot ‘em ups are still being made.
Shoot ‘em ups are normally a fun diversion for a game, but due to their age and memory limits they tend to have only a couple hours of fun involved in them. More recent games tend to be harder. Gradius 3 for the Super NES has a much longer game with graphics that blow any old arcade games away.
Shoot ‘em ups now can normally be found in the corner of the arcades that is reserved for the "ancient" machines. They tend to be under used but private collectors can find them for a price.