A first-person perspective game where the player directly controls his or her avatar's movement, and, well, shoots things. Alternately, games descended from Doom.
A first-person shooter is not a lightgun game, as the player lacks actual control of the character's movements. (Capcom's Gun Survivor series is a grey area.) Also, third-person games using a camera in tow of the main character, such as Tomb Raider or SOCOM: Navy Seals, are not first-person shooters, also such games often share many elements with FPSes. (Hitman 2, with its mixed modes, is another grey area.)
The stereotypical first-person shooter: the protagonist is in a (para)military, espionage, or police role, armed with an arsenal of a half-dozen to a dozen weapons, ranging from sidearms to anti-tank weapons to alien/high-tech coherant energy weapons. The player travels through military installations, dungeons, caverns, castles, or any other setting that allows for mazes of twisty passages (all alike, of course), slaying anything they come across. Occasionally, a door is locked; somewhere there is a key or a switch to open the door, allowing continued progress. The enemies get tougher as the game goes on, usually due to some plot contrivance; this isn't a problem, as weapons get more powerful to match.
A typical FPS is controlled by the traditional wasd arrangement for movement and the mouse to aim, with the number row used for selecting weapons. This is nearly universal with PC FPSes after Quake.
While it was preceded by a handful of games meeting the basic criteria of the genre , the game that every modern first-person shooter was inspired by, directly or indirectly, is id Software's Wolfenstein 3D. BJ Blaskowitz's dungeon-crawl beneath Nazi Germany set the most basic conventions of the genre, particularly cheat codes (a must, particularly a God mode invincibility code), the screen layout (the weapon is visible at the bottom center of the screen, with a status bar at the bottom or top of the view), and the arsenal (a melee weapon, a pistol, a handful of rapid-fire weapons, a missile launcher, and a flamethrower).
The game that blew the genre open, however, was Doom. Unarguably the most successful shareware game ever, this oft-pirated game was the story of a nameless space marine's travels from Deimos through a portal into the very heart of Hell. Mindlessly violent (it was major news for its gratuitous violence at about the same time as Mortal Kombat) and utterly cathartic, it spawned a raft of imitators of varying quality, as well as a sequel and a half. Doom introduced circle strafing and areas with different elevations (although true 3D level design would come later), and gave people the first taste of Deathmatch head-to-head multiplayer.
After Doom's release, two games were released that, while having little immediate effect on the genre, would go on to plant the seeds of later revolutions. Marathon, released by Bungie Software, introduced dual-trigger weapons (later an Unreal trademark), stealth, and involved, conspiracy-driven storylines (which would become common in later stealth-oriented FPSes.) Descent introduced true 3D level design and polygonal characters, although it's only arguably a FPS.
Doom and Marathon also introduced a new phenomenon to computer games in general; modding. Both games had tools for players to create new areas and levels, and the fans took up the challenge, making new scenarios, sometimes even superior to the original games. This would become common in later games, to the point where some games were superseded in success by fan-made mods.
Quake, however, was the next landmark. Stylistic, violent, and surprisingly scary, it set the new standard, both in level design and technological design. Using true 3D level design, polygonal characters and enemies, and a more realistic physics engine, all later games would imitate it. More important than Quake itself, however, was QuakeWorld, a series of patches for Quake to allow online multiplayer. This would become the killer app for first-person shooters.
Quake, again, inspired a handful of sequels and imitators. This subgenre of Quake-spawned FPSes is almost a genre unto itself, with a set of conventions. Weapons have become more powerful proportionally and better balanced against each other, to discourage players from always using the same weapon. Online multiplayer has become more and more important, to the point where the single-player mode is basically dropped in some games.
The big revolution for deathmatch FPSes came, of all places, from a mod for Quake: Team Fortress. Team Fortress introduced a heavy emphasis on team play, particularly with capture the flag scenarios. Every deathmatch FPS that followed had team modes of some kind, and Counter-Strike and Tribes would focus heavily on such team modes.
A handful of other games introduced small elements that would become commonplace. Marathon introduced deal-trigger weapons (for example, an assault rifle with an attacked grenade launcher), what would become an Unreal trademark. Tribes introduced pilotable vehicles, something Halo and Battlefield 1945 would refine. Goldeneye introduced sniper scopes, such a nifty idea that nobody could figure out why it hadn't been done before. Marathon introduced and Quake popularized rocket jumping, the practice of boosting a jump with an explosion.
The Wolf 3D - Doom - Quake "bloodline" of first-person shooters isn't the only one, however. The genre has diverged at several points.
The first, and least divergent, is console first-person shooters. The most obvious and important change is the controls; with only a few exceptions, console FPSes cannot be controlled with mouse/keyboard, for obvious reasons. Turok: Dinosaur Hunter set the standard nearly all later games would follow, with the left control stick used for movement and strafing, and the right side controls used for aiming. Given the oddball arrangement of the Nintendo64 controller, this set was actually an alternate mode for controls. The twin control sticks of the DualShock PlayStation controller helped encourage the standardization of this arrangement.
Because of this arrangement, and the imprecision of aiming that it brings, auto-aim is very common in console FPSes, balancing out the jerkiness of trying to aim with an analog thumbstick.
After that, no real absolutes can be said about console FPSes as a whole. By and large, they lack online multiplayer; only Quake III for the Dreamcast and Unreal Championship for the Xbox have this feature, although kludges exist for Halo and Timesplitters 2, for various reasons. Generally, multiplayer is on a split-screen, something that annoys PC FPS veterans to no end.Console first-person shooters didn't regularly have online multiplayer until Xbox Live became popular, although there were earlier exceptions on the Dreamcast and PlayStation 2. No single FPS set the standard, however; console gamers play a wide range of shooters, depending on taste.
What sets console FPSes apart from their PC counterparts is the predominence of interesting multiplayer modes in console FPSes. Console FPS multiplayer is much more of a party game, and ever since Goldeneye's variety of weapons and modes, heavy customization in multiplayer has become one of the marks of a quality game.
Unfortunately common in console FPSes is jumping. While jumping has been in FPSes since Rise of the Triad, quite a few mediocre console FPSes have had jumping from platform to platform. Generally, this means "falling a lot and throwing the controller." Not fun.
Another divergent thread is stealth FPSes, or role-playing FPSes, or, most commonly, whatever-the-Hell-it-is-that-Warren-Spector-is-doing-at-the-moment. Best represented by System Shock and Deus Ex, this subgenre focuses on stealth and story-telling, often with multiple paths to accomplish the objectives.
Eidos seems to be the only company really exploring this subgenre, not only with Spector's Deus Ex and Thief: the Dark Project, but with Hitman: Codename 47 (and the far superior Hitman 2: Silent Assassin).
Heretofore unknown Ubi Soft had a hit on their hands when they released Rainbow Six, a highly realistic team-based tactical shooter (as the genre would become known). This subgenre focuses on small teams (with the rest of the team controlled by orders, rather than directly) and rigorously realistic scenarios, usually counter-terrorist ones.
Ubi Soft pretty much has a lock on this genre, with Rainbow Six and its sequels, Rogue Spear, The Sum of All Fears, and Ghost Recon, but Sony's SOCOM: Navy Seals (not a FPS, but part of this subgenre) and, the US Government's America's Army have challenged Ubi Soft's stranglehold of late.
A handful of FPS for newcomers to the genre:
- Quake - Available for everything but your toaster, usually for very little or even free, this is the game that inspired everyone but Warren Spector. Plus, it's hellaciously fun.
- Half-Life - Heavily story-driven, it wasn't the first FPS to incorporate more than just mindless violence, it was certainly the most successful. Plus, Half-Life has arguably the best mods ever created, games like Day of Defeat, Team Fortress Classic, and Counter-Strike.
- Goldeneye - The One True console FPS. This game, with its interesting and varied single-player campaign and its amazing variety of multiplayer modes, is the game that all the competition is still trying to catch up to. Its sequel, Perfect Dark, is arguably superior in single-player, but the multiplayer suffers from the technical limitations of the N64. (Don't let anyone tell you Timesplitters 2 is better, either.)
- Marathon 2 - Mac-only and now sadly dated, this little-known FPS has story, level-design, and style to spare. It's worth it if you have an '040 box laying around, or head over to the Aleph One project at http://source.bungie.org.
If I didn't mention your favorite game, of course, it means I hate you.