The concept for a remake of Half-Life started in 2004 when a group of modders and displeased fans decided Half-Life Source was a bad port, and didn't make full use of the Source Engine's capabilities. In the beginning, 2 seperate teams had formed for the project, Leakfree, and the Half-Life: Source overhaul Project, both with the ambitious goal or recreating Half Life from scratch. Upon finding out about each other, the 2 teams merged together, and the Black Mesa: Source mod was created in 2005. They have, however, since dropped 'Source' from their name at the request of Valve, and are now simply known as 'Black Mesa'.
Since then, Black Mesa has become one of the largest mods ever made, a complete stand-alone game recreated with almost all custom content. The mod has been in development for 5 years and has won 4 awards and 3 honorable mentions.
Black Mesa is set in and around the Black Mesa Research Facility as depicted in the original Half-Life game.
The majority of Black Mesa takes place in the Black Mesa Research Facility, a massive Research and Development lab built on the remains of a Cold War era Missile Complex in the New Mexican desert. The Black Mesa Corporation is a privately owned company, funded by the US Government. The Black Mesa Research Facility is home to just about every type of Scientific Research. Everything from basic science, to teleportation, to aliens are being studied in the compound. Employees live and work at the base, which is kept alive via Railroads used to bring in supplies from outside world. Black Mesa is kept safe and secure by it's remote location, heavy doors, and a large team of armed and trained Security Officers.
In this base, the player will fight through Laboratories, Offices, Tunnels, Warehouses, Surface Areas, Sewers, and Silos. All the while facing heavy opposition from both large numbers of Aliens, and the might of the US Military. Later in the game, the player is transported to Xen. Little is known about Xen or how it will appear in Black Mesa, as the devs have been very secretive about this part of the game.
Black Mesa intends to keep all the original enemies, and has stated that new enemies are not likely. Most enemies in Black Mesa have been recreated and remade. The only exceptions are the Headcrab, and the Barnacle, both of which appear and behave exactly as they did in HL2. Vortiguants look much like they did in EP2, with a slightly modified appearance. Many of the enemies have been made more challenging to fight thanks to better AI and health / damage tweaks.
Each squad has a commander who leads the troops, and killing the commander will result in the other soldiers becoming less organized and effective. Many HECU Squads will also have Combat Medics which will heal their allies in battle, as well as defend themselves if they need to. It has also been implied that HECU Soldiers may not fall for Trip Mines.
There will not be any new enemies, or enemies added from other Half-Life games or expansion packs.
Weapons and Items:
Black Mesa will have most of the original weapons from Half-Life with new sounds, models and animations. A few exceptions are the M198 Howitzer, and the M20A1 FLASH, having both been replaced by the BGM-71 TOW. Ammo counts have been changed as well for balance reasons; The shotgun no longer carries 125 round, but is now limited to 30. The Grenade Launcher only holds 5 shots instead of 10. Larger weapons include M2HB Heavy Machine Guns, Weapon Emplacements, and a device for calling in Mortar Strikes.
Items in Black Mesa include the H.E.V. Suit, Health and H.E.V. Chargers, Ammunition, Health Kits, Batteries, TOW Missiles (around launchers), various Explosives, Weapon Boxes (on Xen only), and hundreds of new props.
Co-Op gameplay (though it is unsure whether it will be done)
Face Creation System
NPC Dynamic Interaction System
Original Music by Joel Nielsen
And much more.
For more information, visit the Black Mesa wiki, check out the FAQ, or visit the Forums.