A video playthrough and review by Medve:
No, Station 51 is not Area 51, and has no aliens, what a bummer. BUT, there are Combine soldiers...and a lot of 'em. Yes, mostly you are going to shoot innocent soldiers, who are just doing their job (spoiler alert: trying to kill you), but you will also encounter some zombies and Xen creatures.
The strongest part of the map is probably the layout. It's not too linear, and keeps it interesting with secrets. It keeps your attention, and of course you don't have to find small objects in big warehouses (which is kind of a fashion nowadays). It's one bigger map, not even sure how did he manage to create such a big map in this engine, but in the end it takes about an hour to finish. Short, logical, has secrets, has plenty Combine to kill. If you haven't played it yet, go ahead.