This mod is based on the old Half-Life 2 storyline, but instead of using the original HL2-wc-maps sources, it's authors are creating all of the maps from scratch, and thus are not limiting themselves in their creativity.

Installation: Put the "darkinterval-beta" folder from the archive into your "sourcemods" folder. Then turn on the "upcoming-" function in the "Betas" option of your Source SDK Base 2013 Singleplayer in the Steam tools list and restart.

Discussion thread
Dark Interval on ModDB