About the pin: Pc have to make a panic roll, NPC lose a slow action. Aliens are neither. So i presume that they're not affected. They follow their own rules, like monsters in Forbidden Lands.
Everyone obviously can think what he prefers, but what i'm saying here is that:
Alien can and ARE deadly even if you presume that soldiers with their weapons can kill them like in Aliens. It's written that normal people could just dream about getting hands upon a military weapon, so the "magic" of the horror, fear, terror of the civilian character holding an improvised weapon or a simple civilian gun it's already there.
I'm just saying that when a combat between marines and aliens will finally come i think that following the rules will be very weird. Colonial marines are only portraied in "Aliens" and it makes really no sense to change the overall feeling of it. As a player it would be a let down if it would take some rounds in 3 soldiers to kill just an alien, as i said.
The overall round would be like that, assuming that the marine won the initiative (unlikely because aliens draw 2 initiative cards and act twice as you all know). He shoots, the Alien is wounded, he run to the marine (movement 2... from short to arm's reach), and attack twice. If the armor of the marine kicks in and he's not dead or incapacitated he would have to shove him and shoot, and wounding it again, and again he will recieve other attacks from the beast etc...
I dont really care about bonus dice from panic, full auto, weapon spec as long as they dont reach 30-35 which is the way to go to have some hopes to come out from such a situation. And i'm afraid that this is rather a big problem for me and for those that love the sequel at least the same as the original.