Operation: Black Mesa is a fan-made reimagining of Gearbox's Half-Life™ Opposing Force and Half-Life™ Blue Shift.Two Campaigns in OneExperience two unique single-player campaigns taking place during the Black Mesa Incident that started off the events of the Half-Life™ universe. Survive a day job gone wrong as security guard Barney Calhoun. Escape the doomed facility after a FUBAR'd mission as Corporal Adrian Shephard of the Hazardous Environment Combat Unit.Features Two single-player campaigns featuring expanded gameplay and new content. A plethora of engine enhancements and new graphical effects. The Source engine looks better than ever. Fast-paced combat with over 30 unique enemy types - Run. Think. Shoot. Live. Over eighteen weapons suited for all play styles. How will you survive Black Mesa? Original music. Two games - two soundtracks. Expanded narrative elements to connect with established Half-Life™ lore. Customize the game to your liking with a mod-friendly set of tools.