I have changed the engine for Half-Life 2 episode one because of the env_cubemaps would not work. Everything was bad so I tried to half-life 2 episode one engine, and it seems to work. So now the game runs at half-life 2 episode one engine.
In this mod you play as part of the Combine. Your objective is to defend citadel in City 17 from the hoards of Zombies and rebels. You start under the city and work your way to the surface, from there you move onto Ravenholm and then you acquire a vehicle and travel through the sandtraps. Onto Nova Prospekt and back to the city again. Your final act of defensive is the sacrifice of the Citadel City itself - You must destroy it rather than let the Zombies and rebels take control.
Awesome and you just gave away the ending :(