I've been playing Black Mesa, and I've gotten up to Xen, and I have to say that they've done an outstanding job.

They've managed to make it feel alien, while also expanding on the mechanics of the core game.

It's beautiful, and (most importantly to me) it actually makes the story behind xen more clear.

The scientists at black mesa were already sending survey teams to explore xen, and while that's said in some side dialogue in half life 1, you never really saw it.

(cont)