Black Mesa: Blue Shift

"'Barney Calhoun is not having a good day.""First, he's stuck in his usual dead-end job at a government facility he's pretty sure isn't entirely legal. Then he gets in trouble with his boss when he gets blamed for some minor lighting issue. Then he's forced to force his way into a crashed elevator on the other side of the facility, where some jerk called Rosenburg is stuck because he tried to rewire the thing himself. THEN he winds up having to take care of Dr. Rosenburg, who's hurt his leg, and carry him all the way back while having to put up with the cretin whining, demeaning him, and generally being a nuisance.""And just when things seem like they can't get worse, something goes wrong in one of the labs.""Now the majority of the workers at the base are dead. The phones are all out. All contact with the surface's gone. Hostile aliens are pouring into the facility, killing humans and each other in a all-out war for supremacy. The military's been deployed in to kill everything there - including the innocent scientists and security guards. THEN some kind of black ops unit is deployed in to kill EVERYTHING - including the already murderous soldiers. There's no help coming.""It looks like the only way out is through. Barney's got a gun, armour, supplies, and all he needs. And he's going to fight his way out of this nightmare, even if he has to drag Rosenburg all the way with him.'""- Description on Steam page"Black Mesa: Blue Shift is a concept for a add-on expansion pack for Black Mesa, the third-party remake of Half-Life. Similar to the base game being a remake of Half-Life, it is a remake of Half-Life: Blue Shift, a expansion pack for the original Half-Life. The game revolves around Barney Calhoun, a security guard at Black Mesa and a friend of Gordon Freeman's. When the Resonance Cascade occurs and enables an alien invasion of the facility, Calhoun must fight his way to safety and rescue the scientists and fellow workers trapped within the base before escaping.

Gameplay
The gameplay of Black Mesa: Blue Shift is almost identical to the gameplay of the base Black Mesa, being a first-person shooter where the player combats enemies, navigates environments, solves puzzles and carefully monitors their ammunition supplies. Compared to Black Mesa, Blue Shift has a much greater emphasis on character interaction and story progression, featuring occasional third-person cutscenes and the player character making much more dialogue than usual. Assistant characters also appear much more frequently than in the base game, and maintaining their lives is more vital than ever. The player is also given frequent interaction with a non-player character, Dr. Rosenburg, who often requires protection and escorting, and can assist the player at certain points. Aside from these changes, gameplay is mostly the same, with continuous progression through environments and usage of terrain over firepower when fighting enemies. The expansion pack also features significantly different weaponry and pickups compared to the base game.

Weapons
The weaponry of Blue Shift is significantly different than in the base game, with only one weapon being relatively unaltered in the add-on. Many weapons either have had their functions radically changed or been replaced with different weapons.
 * Nightstick: Replacing the Crowbar, the Nightstick is the main melee weapon of the game, given to Calhoun as he begins his duties. The main change made is that the Nightstick, when used, can apply a electrical shock to a organic enemy, temporarily stunning them for a easier time dispatching or avoiding them.
 * Glock 17 Pistol: The only weapon left mostly unchanged, acquired at the start of the game and functioning as Calhoun's main sidearm. The main changes made are that it cannot rapid-fire, and instead has a detachable silencer that can be attached to the weapon to improve its accuracy. It can also carry 20 rounds in its clip instead of 17.
 * Desert Eagle: Replacing the 44 Magnum Revolver, the Desert Eagle functions as a stronger Glock 17 with less ammunition available, requiring it to be used to deal only with tougher enemies. Unlike the Magnum, it has a clip size of 9 instead of 6.
 * MAC-10 Submachine Gun: Replacing the MP5 Submachine Gun, the MAC-10 is obtained
 * Ithaca 37 Shotgun: Replacing the SPAS-12 Shotgun, the Ithaca 37 Shotgun is first acquired from the destroyed Black Mesa Guard Range. It functions similarly to the SPAS-12, with the main differences being that it is more accurate and its secondary fire is changed from a double-barrelled blast to allowing Barney to look down the Shotgun's barrel to make a shot even more accurate.
 * Tranquilizer Rifle: Replacing the Crossbow, the Tranquilizer Rifle is first acquired from the dead scientist found when the Ichthyosaur is disembowelled.
 * Grenade Launcher: Replacing the RPG,
 * Sigma Laser: Replacing the Tau Cannon, the Sigma Laser is a older prototype of the Tau Cannon first acquired from the scientists
 * Lightning Gun: Replacing the Gluon Gun,
 * Chumtoad: Replacing the Hivehand,
 * Energy Grenades: Replacing the Frag Grenades,
 * Pipe Bombs: Replacing the Satchel Charges,
 * Flamethrower: A entirely new weapon first found in
 * Another entirely new weapon

Ammunition

 * 9x19mm Parabellum Rounds: Ammunition for the Glock 17 Pistol and MAC-10 Submachine Gun. It comes in five different types.
 * Pistol: A handful of Pistols can be acquired from dead security guards, HECU marines and Black Ops assassins. Collecting it gives the player 10 9x19mm Parabellum Rounds.
 * Pistol Clip: Pistol magazines found throughout the facility and its surroundings. Collecting it gives the player 20 9x19mm Parabellum Rounds.
 * SMG: Submachine Guns can be acquired from dead HECU marines and Black Ops assassins. Collecting it gives the player 25 9x19mm Parabellum Rounds.
 * SMG Clip: Submachine Gun clips found in areas where the HECU and Black Ops dominate. Collecting it gives the player 50 9x19mm Parabellum Rounds.
 * Bullet Box: A rarely found large box of 9x19mm Parabellum Rounds. Collecting it gives the player 200 9x19mm Parabellum Rounds.
 * .357 Magnum Rounds: Ammunition for the Desert Eagle and . It comes in three different types.