Half-Life: Opposing Force

Half-Life: Opposing Force is an expansion pack for Valve Software's science fiction first-person shooter video game Half-Life.

Opposing Force returns to the same setting as Half-Life, but instead portrays the events from the perspective of a U.S. Marine, one of the enemy characters in the original game. The player character, Adrian Shephard, is sent in to neutralise the Black Mesa Research Facility when a scientific mishap causes it to be invaded by aliens, but quickly finds that the Marines are outnumbered and slowly being beaten back by a second alien race and black operations units.

Inside Mepaces-Nebula
The game Half-Life: Opposing Force hasn't actually been played-through on any of the member's channels but Will owns a Steam copy and has completed the game along with Half-Life and Half-Life: Blue Shift but not filmed. Will has an active playthrough series of Half-Life: Blue Shift on the "Mepaces Will // Will's Music" channel. Opposing Force will likely be played through on the channel after Blue Shift is completed then the original Half-Life after Opposing Force has been completed.