Station 51 is a single player mod for Half-Life 2: Episode 2. You are on the run from the Combine closing in on your outpost. Can you escape?
I have to say a good mod in general.
Why I give it an 8/10 is because:
Pros:
-Good detail in most parts of the maps
-Straight-into-the-action type, no need for tutorials
-Overall fun experience
Cons:
-Repetitive gameplay, same enemies in the same kind of environment
-No story, wich makes your efforts feel useless in the end
-Lack of puzzles and/or events that take time
I personally like to see much custom content into mods, for example custom guns, vehicles, sounds etc.
Anyway, I say 8/10 and great job on this!