opposingforce

Opposing Force is a 1999 first-person shooter expansion pack for Valve's Half-Life. Developed by Gearbox Software and published by Sierra Studios, it runs on the GoldSrc engine and was released as a standalone expansion that integrates with the Half-Life storyline. The game introduces a separate perspective within the Black Mesa Incident.

The player character is U.S. Marine Corporal Adrian Shephard, assigned to contain and cleanup the disaster at Black Mesa. The narrative unfolds in parallel with Gordon Freeman’s actions, offering additional backstory and viewpoints on the facility's collapse. Players encounter new environments, scenarios, and factions, including military personnel and alien forces, which expand the scope of the original game without altering its core mechanics.

Opposing Force adds new content such as environments, enemies, and narrative-driven sequences that deepen the Black Mesa saga. It also introduces new weapons and equipment for the protagonist, contributing to varied combat approaches while preserving the gameplay style of Half-Life. The expansion is designed to complement the original campaign, providing fans with a different lens on events surrounding the Black Mesa Incident.

Reception to Opposing Force was generally positive, with praise for its cohesive tie-ins to Half-Life’s storyline and for expanding the setting with fresh encounters. Some criticisms noted its shorter length relative to the core game and its dependence on familiar Half-Life mechanics. The expansion has since been included in various compilations and remains a notable entry in the Half-Life series, illustrating Gearbox’s early collaboration with Valve and its approach to expanding established game worlds.