Theoretical physicist Gordon Freeman arrives late for work at the Black Mesa Research Facility. As part of a scientific experiment, he pushes an unusual crystal of alien origin into a machine known as the anti-mass spectrometer. The spectrometer explodes, creating a "resonance cascade" which severely damages the facility and opens a portal to an alien dimension, Xen. The surviving scientists urge Gordon to travel to the surface, where he defends himself against hostile Xen creatures and US marines dispatched to eliminate the aliens and the Black Mesa personnel to cover up the incident.
Half-Life is a first-person shooter (FPS) that requires the player to perform combat tasks and puzzle solving to advance through the game. Unlike most of its peers at the time, Half-Life uses scripted sequences, such as a Vortigaunt ramming down a door, to advance major plot points. Compared to most first-person shooters of the time, which relied on cut-scene intermissions to detail their plotlines, Half-Life's story is told mostly using scripted sequences (bar one short cutscene), keeping the player in control of the first-person viewpoint.
Source: Wikipedia, "Half-Life_(video_game)," available under the CC-BY-SA License.
Microbadge: