A single player campaign. You must fight your way to the surface of Black Mesa...
Better than average HL mod.
Pros: nice level design, attention to details in the first part of the game. The transit zone in the beginning is stunning to see on this engine.
There are some small gameplay related surprises.
Cons: reused design ideas of HL, OPFOR and BSHIFT. No clear story progression - you just wander around completely pointlessly, and then - sudden ending, as if the mod wasn't finished.
Conclusion: mod without any idea, but with great content. I usually play projects which have somewhat good idea but but execution, here I see good execution but no idea (story-wise) whatsoever. There's literally less story in this mod than in DOOM in 2/3 of the mod.