A lot of dead humans.
In ALIENS, the pulse rifles had 10mm, explosive, armour-piercing ammo. Unless at point blank, the comparitively primitive weapons Dutch and co. used wouldn't be so useful. Not to mention that dense terrain with excess cover is the kind of environment that the Alien thrives in, since its angle of attack can never be determined until the last second.
Much like the Predator, it would've picked them off one by one. Except, instead of holding back for the sake of a good fight, it would've simply killed Dutch instantly at the end.
Everything is pretty much set in the Alien's favour, because the Predator and Alien essentially share most of their tactics and we saw how the terrain favoured the Predator.
Be the thunderbolt that strikes from a clear sky - despite the fact that you could easily destroy your enemies in a straight-up fight. That's the common link between the creatures this forum's dedicated to.
In fact, the Alien's lack of pride probably makes it a more effective predator at the end of the day, using the term literally.
