You take the role of Nick Farrel, a technical engineer in Delta Base - the complex that competes with Black Mesa in various research fields including exploration of the borderworld Xen and weapon development. Due to accidental entanglement of two different experiments conducted at the same time the infamous resonance cascade affects the Delta Base as well, bringing the hostile alien lifeforms which infest the facility very soon.
Shame it's bolt-action instead of semi-auto in the final version. The scope's zoom could be better too. It's fun to use, but still.