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'm going to go right ahead and say that I don't remember last time when I played a HL2 mod which kept surprising and challenging me on almost every corner. The gameplay is really great, and I was really surprised how long it took to see the first "Loading" screen. I think the Airboat part might have been a bit longer, but it's being recompensated by being a frequent victim of ambushes. The balance is also pretty good, I spent most of my time using Shotgun and Gravity Gun but there were moments when I was glad that I have found Crossbow earlier in the game. Level Design on it's own is also on a high level, the only thing I could complain about a little bit was separating the map from the skybox with the big rock props which didn't made a lot of sense in some spots, also the factory in the background was mostly flat, I thought it could use some little roofs or whatever to just make them look less dull. But those are details really, overall the game is great and I was VERY pleasently surprised.