In the movie a couple of quick bursts of pulse rifle fire was enough to kill them. It was a little ridiculous in AvP to have to shoot them with 50-odd rounds before they would go down.
The new screens look great, I'm happy with the way the Aliens look, although they are missing the 5th dorsal spine. Mostly I'm glad they're walking on two legs like they're supposed to be, rather than the way they have been portrayed in recent years as quadrupeds.