— Games Radar, "101 things we've learned from games"
A classic staple of The Golden Age of Video Games that has fallen out of favor in recent years. Everything is trying to kill you, and you have unlimited ammunition and a license to shoot first and ask questions later. Frequently, you're flying a spaceship or some other small craft, but other examples of the genre involve abstract shapes, people walking around with guns or bows and arrows, and so forth.
So popular were shoot 'em ups (and their close-combat cousin the Beat 'em Up) that many computer games magazines of the mid-late 80s took to jokingly appending "'em up" to whatever genre of game they were reviewing — puzzle 'em ups, platform 'em ups, quiz 'em ups and so on.
The term shmup is an abbreviation of "shoot 'em up", but is typically used by the fans who coined it to refer specifically to fixed-scrolling shooters that are not three-dimensional. For instance, 1943 would fit this description, whereas Geometry Wars would not (it is free-scrolling according to player movement), and neither would After Burner (it scrolls into/out of the screen in 3D). This kind of restrictive use is, however, debated among shoot 'em up fans.
Power Ups typically increase the power and spread pattern of the primary weapon, which is usually fired continuously from the start of play until the end. Usually, a limited number of screen-clearing Smart Bombs are included to get the player out of a jam in a hurry. Many later games end their levels with a giant Boss Battle.
The actual shooting part can vary in complexity. It can be as simple as holding down the fire button and never letting go or it can be more complex either due to ship's low firepower (e.g. Space Invaders) , scoring systems required to watch what and when to shoot (e.g. Radiant Silvergun) or other reasons.
The Ur Example is quite possibly Spacewar! (although it's more of a one-on-one shooter rather than a shoot 'em up), the Trope Maker is Space Invaders, and the Trope Codifier is Galaga.
Like a platform game, shoot 'em ups have become popular with amateur game developers for their relative ease of development. While very few professional examples of the genre have been developed recently — for example Gradius V, which wasn't developed by series creatorKonaminote (although the company that worked on Gradius V was founded by former Konami employees).
Today, shoot 'em ups in general suffer from terminal It's Short, so It Sucks -itis from many critics. Most of these games are meant to be played in short bursts or in arcades, but if they are played entirely in one go, they would last no more than two hours at best. Worsening the decline is the redefinition of the term "shooter" — no longer used to refer to shoot-em-ups, they now refer to the distantly-related First-Person Shooter genre, or (merely) closer-related Third-Person Shooter.
Life In A Game spoofs them, specifically Star Fox, in Episode 4-2.
A Super Trope to:
Bullet Hell, characterized by very large numbers of slow-moving enemy projectiles, or fast moving on the hardest parts.
Cute 'em Up, cute and silly graphics and sound, although the action and difficulty are no less intense.
Casual Game: Most games in the genre, especially older ones, can be summed up as "move stick/D-pad to move, press this button to shoot, press this button for Smart Bomb, now go kill enemies trying to shoot you." However, some shmups, particularly more modern ones, avert this and go for more complicated gameplay; some examples include Stellavanity, Hellsinker, and the console-exclusive arrange modes of various CAVE games.
Cognizant Limbs: In some shooters, bosses may have certain parts such as limbs or weapons that can be destroyed for extra points. Sometimes destroying certain parts can make boss battles easier while other times it results in the bosses upping the ante. Some games such as Warning Forever center around this trope.
Collision Damage: Generally, touching another airborne enemy will hurt you. Ground enemies can be safely flown over (unless you yourself are also on the ground). Other games, such as Castle of Shikigami and Radiant Silvergun have obstacle levels where you are surrounded by walls and colliding into one will hurt you.
Continuing Is Painful: Using a continue will usually reset your score. This is important, because otherwise a player who can't avoid taking damage will be able to obtain a high score with fairly trivial effort. It also encourages players to go for a no-continue clear (otherwise known as a one-credit clear, or 1CC); it's often argued that a game is only counted as completed if it is done with no continues. A player who "credit-feeds" the game and calls it completed may as well have used an infinite lives cheat.
Deadly Walls: In most games where there are walls, touching a wall will kill you; this is usually justified in that you're flying a ship of some sort and rubbing against solid objects does bad things to your hull. In some other games, such as Super Aleste touching walls is harmless unless you get squashed between two walls or against the edge of the screen. In rare cases, like Hellsinker or Deathsmiles, getting squished doesn't even hurt you at all, and you'll simply "snap" to where there is open space.
Drop-In-Drop-Out Multiplayer: Often, shoot-em-ups will have support for two simultaneous players, with a second player allowed to join at any time. As a courtesy, it is recommended that you ask before joining in on someone's game.
Endless Game: Older games tend to go on forever (or until you hit the Kill Screen, if one exists), either in the form of ever-toughening waves or looping stages that increase in difficulty with each new playthrough. A few newer games, such as Eschatos and Warning Forever, do feature endless modes, however.
Every 10,000 Points: The usual method of obtaining a 1-Up. Some games will offer a 1-up every x points, so as long as you keep racking up points you'll gain more one-ups. Some others will only offer one or two extra lives, and some will only offer it as an item or not at all.
It's Up to You: Often, the plot states that the player character is the only one capable of taking on the enemy fleet.
Life Meter / One-Hit-Point Wonder + Video Game Lives: One or the other; if you have a lifebar, the game typically ends once you empty out. If you have only one hit point, you usually get multiple lives, although some games allow you to set the number of starting lives to one. A few titles, such as 1942 Joint Strike and Kamui, offer both a lifebar and multiple lives.
Characters with Spread Shots can easily hit the entire screen, but in exchange have a hard time with a lone and durable enemy, and will often have the speed of a turtle. The damage concentration problem can sometimes be solved by moving up close to the target, but one greatly risks a shot to the hitbox by doing so.
Characters with linear shots can easily destroy strong enemies without having to point-blank the target. They will also have fast speed, allowing them to zip around to destroy multiple enemies, pick up items, etc. However, hitting anything to the sides will require the player to move a lot, and the fast speed may make precision maneuvers difficult.
Characters with homing shots can simply "fire and forget" whether the targets are spread out or in one spot on the screen. But homing-shot characters also tend to have poor damage output and slow speed, making them Awesome, but Impractical sometimes.
Nintendo Hard: The genre is well known for its relentless challenge, especially since it has its roots in arcade games, where difficulty is necessary to allow players to eventually put in more coins or hand the machine over to the next player and their money, generating profit for the arcade. Modern Bullet Hell games, particularly their True Final Bosses, contribute to the genre's "oh my god this crap is bloody impossible" image.
Power-Up: Often by destroying unique item enemies. Some other games use Experience Points, and a few games, even modern ones, eschew powerups altogether.
Scoring Points: A staple of the genre. Older games typically just amount to "kill enemies and collect point items", but newer games generally have more complex scoring systems, sometimes requiring dexterity or a guide to figure out.
Smart Bomb: In older games, these are intended as offensive weapons; it wasn't until the mid-90's that developers started taking their use as emergency defense rather than firepower into account. Generally, the rule of thumb is to avoid using them unless you're in a tight situation, but some games, like those developed by Shinobu Yagawa (e.g. Battle Garegga, Ibara) encourage you to bomb all over the place for bonus points.
Spread Shot: A common type of weapon. Generally great against large crowds of enemies but lousy for bosses and other situations demanding precision. Characters and ships that specialize in spread shots tend to move slower as well.
Turns Red: As you chip away at a boss' life bar, once it hits a certain threshold they will take on a new form with more difficult attacks patterns. Although this has been seen in some older shoot 'em ups, it has become a commonplace in modern shooters, especially with bullet hell ones.