Half-Life: Opposing Force follows the character Adrian Shephard, one of the Marine Corps Hazardous Environmental Unit Commandos, who was sent in to exterminate everyone at Black Mesa Research Facility and the Lambda core, and ultimately to exterminate Gordon Freeman in particular. However, Shepard never really receives these orders; he is separated from his unit early in the offensive, and attempts to reunite with his squad for the first part of the game. He finally reconnects with his squad, but is left behind when the mass evacuation of the facility begins. Shepard, along with other soldiers left behind, attempt to find a way out of the facility, expressing their lack of enthusiasm for their orders.
Shepard ultimately catches up with Freeman, and watches as he enters the Xen relay and escapes from Black Mesa. Shepard experiences the previously un-encountered Race-X, a species of alien who came to the facility after Freeman had left. He travels to Xen, like Freeman, and succeeds in navigating the hostile environment. Ultimately, Shepard encounters the mysterious G-Man, who compliments him on his resilience and adaptability in such dire circumstances. Unlike Freeman, the G-Man does not offer Shepard employment, and instead leaves him in stasis on a tram seemingly careening through outer space. Shepard's ultimate fate is unknown; he has not explicity died, but has yet to return to a later instalment of the series.
In order for parts of the story to make sense, some weapons and even some enemies were entirely different, and replaced items from Half-Life. For example, the HEV suit was removed and replaced by Body Armour, which functions the same by makes sense when put in context of the story, Adrian Shepard would not have access to the same technology that Gordon Freeman would. The game also introduced new AI system, and a new type of Black Mesa guard, named Otis who, armed with Desert Eagle, provides significantly better support than " Barneys" who only had the basic pistol. Opposing Force's new interactive AI system allowed fellow troops, like Medics, to heal the player character and basic Soldiers would toss them ammo.
The Crowbar which became an icon of the Half-Life series was not actually taken up by Adrian Shepard, instead replaced by the Wrench. The Wrench is significantly slower than the Crowbar was, although much more powerful. In addition, the Wrench actually had an alternate fire, which readied the Wrench for a more powerful blow by winding it up for a moment. The Wrench is the first weapon Shepard obtains through the events of Opposing Force.
Shepard actually gains an additional melee weapon along with his Wrench, a Combat Knife, which is actually less powerful than either the Crowbar or Wrench, but has a much faster attack rate. Additionally, if Shepard is able to sneak up on an unsuspecting enemy, the Knife should be able to deliver a one-hit kill.
The Colt Python of Half-Life was replaced with the more militaristic Desert Eagle. The two are quite comparable in terms of high-power, accurate weapons, but the Desert Eagle sacrifices the Python's zoom feature for a laser sight, triggered using the alternate fire button.
Keeping with the military theme of Opposing Force, the Crossbow is replaced by a tactical bolt-action Sniper Rifle, which was quite similar, in many ways, to the Crossbow of the past. First introduced in the training sequence at the start of the game, it too featured a zoom feature for long-range enemy elimination.
M249 SAW Light Machine Gun
Another military weapon, Opposing Force features a SAW LMG, which has both a rapid rate of fire and massive clip size, and is quite useful for engaging multiple targets or laying down suppressive fire.
The experimental weapon featured in Opposing Force appears to be some sort of portable teleporter, or some early attempt at one. However, Shepard uses this experimental technology for more macabre purposes, and uses it as a weapon. Its primary fire launches a portal torwards an enemy, and teleports them far away from Shepard, or destroys them (the technology is unstable, after all). It's alternate fire transports Shepard himself to Xen, for good or bad. Teleportation can either kill Shepard or help him move past an obstacle.
This expansion also introduced a host of new Alien weaponry, including the Barnacle, which is essentially a hand-held version of the Barnacle enemy encountered many times in the game. Firing the barnacle launches it's long tongue at a target enemy, dragging it close and dealing damage until it is fully digested. It is also used as a method of travelling across otherwise inaccessible gaps, by attaching its tongue to specific, stationary spores and dragging the player closer to the targeted spore.
Speaking of Spores, another new Alien weapon was just that, a living weapon which fired spores at enemies. The spore launcher actually swallows the ammo fed into it, and spits out the explosive ammunition upon command. By holding down the alternate fire, the Spore Launcher charges up a shot before firing it. Spores actually bounce a bit if not targeted directly at an enemy, so take careful aim.
Another living weapon, the Shock Roach is a giant bug that fires electricity at enemies. Like the Hive Arm it replaced, the Shock Roach regenerates ammunition up to eight shots, but each shot does less damage than the preceding one. It is not recommended firing this weapon underwater; it is instant death.
Though it wouldn't make much sense for Adrian Shepard to be wearing the HEV suit worn by Gordon throughout Half-Life, the same system takes place, by charging Shepard's high-tech Body Armour, much in the same fashion one would charge the HEV suit. In fact, the Body Armor charges using either specifically Body Armour chargers or the more common HEV charging stations throughout the Black Mesa Facility.
Unlike the HEV suit, Shepard's Body Armor does not come equpped with a flashlight, and he must instead rely on his helmet and Night Vision to illuminate the darker corners of Black Mesa. The Night Vision is used in essentially the same way the flashlight was in Half-Life.
Opposing Force introduces a new AI system, and allows the player to have a squad of allied soldiers, who can assist in various situations and provide additional fire support. There are several different classes of soldiers, all of which are able to assist Shepard in various ways.
Just a typical grunt, Soldiers are best used to provide additional fire and protection against the many hazards of Black Mesa. However, they can occasionally provide ammo to Shepard when needed.
As the name says, Medics can provide healing in addition to standard soldier duties. This makes Medics one of the more valuable allies to have around, as they can keep Shepard healthy and happy. Occasionally, a Medic can be required to move the plot forward, if there is a soldier who needs medical attention in order to open a blocked path, though for the most part they are not necessary to keep around.
Soldiers that carry a blow torch and supplies, these chain-smokers can break through otherwise inaccessible doors, either to advance the plot, or occasionally, to open up a secret area (usually by keeping them alive for a long period of time). If an Engineer encounters a door, he should automatically attempt to break through, unless there are enemies nearby that must be taken care of.
- Jon St. John, the voice of Duke Nukem, lent his voice for senior drill instructor Dwight T. Barnes and various marines in the game.
- Michael Shapiro is the voice of Barney Calhoun.
- Harry S. Robins provided the voice for various scientists.
Minimum: 500 mhz processor, 96mb ram, 16mb video card, Windows 2000/XP, Mouse, Keyboard, Internet Connection
Recommended: 800 mhz processor, 128mb ram, 32mb video card, Windows 2000/XP, Mouse, Keyboard, Internet Connection