A single player campaign. You must fight your way to the surface of Black Mesa...
Playing this from the first release in 2002, it's amazing how many maps have been brought to life in the name of the Residual Series.
Having played through the latest build, I'm still awestruck by the level of detail while still retaining the class atmosphere and design of Half-Life.
There are some discrepancies, such as low-def and high definition models mixing and with multiple routes I have to say I got lost on a few occasions, but these are slight blemishes on a massive project.
Absolutely phenomenal work. I hope the author still has a few maps up his sleeve for future releases! :)