Mission Improbable is a singleplayer mod for Half-Life 2: Episode 2. In it, Gordon Freeman is tasked with re-activating a Resistance listening post. From there, things quickly escalate.
Closest to Episode 3 as you're gonna get. You perfectly managed to capture the look and feel of half-life. It just feels like Valve made it. Which says a lot. This is the quality a game should have let alone a mod. Another person that should be hired by Valve :D
This is the first mod I've downloaded from ModdB, and holy **** is it good! Very professionally done! If this weren't in essence, Half-Life 2, this could pass for a believable single-player campaign of a completely different game. I absolutely LOVED the outdoor enviroments. Those are what made the campaign so believable for me.