As described, I remember playing a game like this ages ago.
The variety came from the scenarios, not the aliens; crawling through tunnels, crossing a nest, defending a lab, etc. Also you had different kinds of gear (flamethrowers, guns, gernades, etc) and different melee skill on each grunt.
It was a redo of the aliens movie.
Is this just that, but with minis?
Anyhow it was good fun.