Delta Particles is a single-player modification for Half-Life.

The plot takes place at the universe of HL. You're playing as a technical engineer of complex "Delta Base" Nick Farrell. Unfortunately, the protagonist was in the wrong place at the wrong time, as an experiment at theBlack Mesa Research Facility resulted in a resonance cascade that teleported extraterrestrial beings from the world of Xen to Earth.

Features:

• A new single-player campaign consists of 4 chapters, comprising 35 maps

  This is a long single-player campaign lasting from 3 to 6 hours. New story, characters and adventures are waiting for you!

• Total conversion, a lot of new content

  New textures, sounds, models, and other assets are included. Delta Particles is completely base on new assets!

• Atmosphere of the new scientific complex "Delta Base"

  A brand-new scientific complex located somewhere in the Nevada desert. "Delta Base" is 
  the main competitor in experimental teleportation research to Black Mesa, because the U.S. government has awarded a grant to develop spatial teleportation devices.
  Visit new locations, from scientific laboratories to industrial areas!

• New weapons

  Your armory includes new weapons and heavily reworked old ones. Now you are definitely locked and loaded!

• New Dark Ambient soundtrack

  It features a new Dark Ambient soundtrack by "Iron Cthulhu Apocalypse" and "Out of Hell". This soundscape immerses you in a deep and gloomy atmosphere of these places.

• XEN maps

  It's XEN. If you like this alien, rocky world from the HL universe, you'll enjoy it!