G-man man is asking you for another mission at Xen, this game is kinda difficult until you realise it. =P
This mod does a lot of things I liked, namely the settings of the maps, the actors being fairly close to their original counterparts, and how much it felt like a Half-Life experience. Unfortunately, there were also many points where I got flat out lost and confused on what to do next. Overall, however, I'd recommend trying it at least once.