I found this fantastic video on YouTube which led me to one of our linked sites, Pryotecto-Yautja. Turns out one of their forum members, Deimos Anomaly, has made this cracking Aliens game using the Doom2 engine:
The game text is in Spanish(I think) and there are only two levels. You don’t need Doom2 to play this, you just download and unzip. As far as I can tell it’s just a demo. If anyone reads Spanish(?), you can check out original thread over at Pryotecto-Yautja.