didn't know being a forum staple was a bad thing
Just make a mechanic that the longer you stay in an area the more aliens come and the bigger aliens. Kind of like the police mechanic from GTA games. Only catch would be standing around shooting them just fits into a horde mode. Day Z / War Z have a lot of stealth with 40 - 60 minutes full of literally nothing, because you're so good at sneaking around nothing attacks you. But as a trade off you're only going half speed. In an Aliens game, making a sound can have a 50% chance of spawning an enemy behind you.
Here's how I'd do an Aliens game. I think you can combine action with survival horror in this case. Have a ship get stranded on a planet crawling with xenomorphs, where no matter how much firepower you have, it doesn't matter because you'll eventually get overrun. In most games, I'd say I'm not a fan of the "infinite respawning" gimmick, but I think it could work here. It'd force you to keep on your feet - you could never just stand your ground and fight them all off. Plus, it'd encourage players to avoid encounters when possible. And there'd be constant dread that an alien could be stalking you at any moment, waiting for the best opportunity to pounce. Point is, you gotta find a way off the planet as fast as possible, and you want to do anything you can to not draw attention to yourself. You know, kind of like you're playing Newt, but with guns. In a jam, you can fight, but ideally, you'd be looking for secret passages, hiding, and always watching over your shoulder.
And heck, this may be cliche, but maybe have other survivors, as well, that you encounter, and you have to make tough decisions. They could be infected and you'd have no way to know - do you risk that? Maybe the person is a hothead - you wouldn't want a companion who fires wildly at the first sign of anything that moves when you're trying to avoid detection - but then, maybe there's an area up ahead where you're forced into an encounter and it'd be handy to have the extra firepower. Or maybe there's someone with useful information, but they're panicky - you'd have to work on keeping them calm so they don't do anything to attract unwanted attention.
Yeah, I know it sounds kind of like "The Thing," video game, and it wasn't all that great. However, I think the basic concept was a very good one, just poorly executed. I'd like to see that idea done right.
How about limiting resources where it then turns into you want that gun, but someone else does too and they're willing to shoot you for it. If not throw a noise maker at you and let the Xenos get you?
I'd think for that idea to work it would need to be an open world or MMO. And what if there was no way off (outside of standard collect parts of a communications relay and assemble it), but rather to ensure your safety you just need to take the fight to the Queen.