Story: After entering the portal at the end of Half-Life you are frozen by the Gman. Many years pass and humans build and occupy a city called Xentopia on Xen. Xen Life forms are captured and held in prison. While citizens of Xentopia continue to live in prosperity, a prison guard finds a blue eyed vortigaunt near the prison. They capture it and put it into a cell immediately. After a few hours later the unique Vortigaunt proceeds to overtake the prison and free all Xen life forms. Xen life forms start to terrorize the city to take their home back. After few weeks later when the city is at the edge of chaos Gman wakes up his secret weapon. Gordon Freeman.
If I were to summarise Xen Assault in a single word it would be this: Frustrating.
The idea behind the mod is pretty unique; Set years after Half-Life, a human colony on Xen descends into chaos after a powerful vortigaunt is captured and proceeds to wreak havoc on the place.
The problem is, other than the skybox and the occasional patch of xen dirt here and there, there isn't really anything unique about Xentopia. It looks like any other city on Earth would. I suspect this comes down to a lack of ability from the author to create a more unique texture set, instead resorting to an overused set of wads by Blazeer (blazurban.wad anf submerged.wad)
The later stages of the demo cram you into some underground sci-fi complex which could just as easily appear in Black Mesa.
On top of all that though, the gameplay is simply awful at times. Once you're out of the tight spaces at the start, you're on the surface facing off against endlessly respawning Race X or Xen aliens, or falling victim to one of the many instant death traps. Then the sci-fi base at the end has you search for incredibly hard to see keycards in fairly dark spaces.
It goes without saying that we won't be seeing a full release of Xen Assault, so the demo is all you get. It's still of a decent length but sadly it's unpolished as it hasn't been properly playtested and adjusted.
For an unfinished beta, this is a stunning lost gem.
I recall downloading this off of an obscure HL forum years ago, and I'm glad to see it has not been totally forgotten and lost to the void of dead mods.
The first batch of levels are equisitely detailed and are a joyous romp to blast through with new weapons at your disposal and plenty of enemies to fight.
While the mod dips in quality near the end and becomes unplayable after a certain point in the adventure, it is still a marvelous overlooked mod that should keep your attention for some time :)