What is Half-Life 2: Deathmatch?

Contents 
1.  Overview
2.  Gameplay
3.  Special techniques
4.  Weapons
5.   Maps   
 
1.  Overview 
Half-Life 2: Deathmatch, abbreviated as HL2DM (or Half-Life 2 DM), is a multiplayer first-person shooter video game developed by Valve Corporation. Released on Steam on November 30, 2004, the game is sold with Half-Life 2: Episode One, and for US$9.99 separately. In addition, HL2DM is sold with Half-Life 2 as part of the Game of the Year package and many of the Valve multi-game packs. On May 30, 2007, Valve made an announcement that Half-Life 2: Deathmatch along with the Half-Life 2: Lost Coast would be made available for free to all owners of ATI Radeon cards, however it later came to light that this free version was distributed without the Source SDK. 
 
2.  Gameplay 
There are two basic gameplay modes: In Deathmatch, each player fends for themselves and attempts to kill as many opponents as possible. In Team Deathmatch, players are assigned to either team Combine (Blue) or team Rebel (Red) and work together to accumulate more kills than the opposing team. In both of these modes, a player gains one point for killing an opponent and loses one point for a suicide. In teamplay servers where friendly fire is enabled, a player will lose a point for killing a member of his own team. The match will end either when time runs out or when one player/team has reached the required preset kill limit. Whichever player or team has the most points at the end of the match is the winner. 

3.  Special techniques  
In addition to the basic gameplay elements, there are several important advanced techniques often used by skilled players.

Gravity Jumping: By standing on top of a physics object and firing straight down at it with the Gravity Gun's primary fire, a player can boost several feet or more into the air. This can be used to quickly move to areas that would otherwise be difficult or impossible to reach.

Fast Balls: By shooting an orb from the ar2 rifle and immediately switching to the Gravity Gun whilst hitting primary fire, the orb can be given an extra boost of speed.

Note: A fast ball, once caught, cannot be fired back at high speed. It will remain fast, however, if it is released with secondary fire.

Grenade Cooking: Also know as "Grav-nading", after using secondary fire to drop a grenade, the player quickly switches to the Gravity Gun and picks it up. The timer on the grenade resets, giving the player additional time to aim and fire it. This technique is often more effective than simply tossing a grenade because it allows the player to have greater control over where exactly it will explode.

Bunny hopping: A type of movement used to move silently, jump over large gaps, and travel even more quickly than regular sprinting. Bunny hopping is performed by sprinting into a circle jump and then remaining in the crouch position while repeatedly tapping the jump key upon landing.

Note: In HL2DM bunny hopping is also commonly called strafe-jumping, speed skating, and overbouncing, however, strafe-jumping is not the same thing.

Rabbit Punch: An object held in the Gravity Gun can be shot and caught rapidly by using primary fire, switching away and back to the Gravity Gun, and then pulling the object back in with secondary fire before it travels out of the gun's range. This is an effective way to reset the timer of an orb or grenade a player is carrying. It can also be used with orbs or other physics objects to repeatedly attack a close opponent without losing the weapon after a single toss.  

4.  Weapons 
The weapons in Half-Life 2: Deathmatch are identical in most cases to those in Half-Life 2, with the addition of the Combine Stunstick and the Selectable Lightweight Attack Munition (SLAM) mine.

By default, a player will spawn with a Gravity Gun, 9mm pistol, submachine gun, and two grenades. In addition, players using a Rebel model will receive a crowbar and players using a Combine model will receive a stunstick. Relative to the stunstick, the crowbar does less damage but attacks faster. Other guns and ammunition are collected as the player moves around the map. Headshots do 3x as much damage as attacks that hit other parts of the body. 

5.  Maps 
Official Half-Life 2 DM maps Name Author Setting (Level from Half-Life 2)

dm_lockdown Valve Nova Prospekt

dm_overwatch Valve City 17 (Follow Freeman!)

dm_steamlab Valve Concrete laboratory resembling Black Mesa East

dm_underpass Third-party City 17 railway

dm_resistance Third-party "Bodies" from Blood

dm_powerhouse Third-party Generic Industrial

dm_runoff Valve Water Hazard

dm_lockdown: This map is set in a dilapidated prison as seen in the single-player chapter Nova Prospekt. As one of the first two officially released maps, it is by far the most often played, especially in league and clan matches.

dm_overwatch: The other map released with the game, this is the most common "king of the hill" style map, especially common in public servers.

dm_steamlab: Based on the map "datacore" from Half-Life Deathmatch, this map was released during an update to help introduce the newly released weapons of crowbar, stunstick, and SLAM.

dm_runoff: Inspired by the map "crossfire" from the original Half-Life Deathmatch, players are able to kill anyone trapped outside of a protected area by launching a missile strike.