I would think the goal of basing off a movie is to recreate the feel of it, and emulate interesting scenes from it. The nature of Aliens was creepy tunnels, fierce enemy, holing up and defending a position, lots of running away, and setting a big bomb. And don't forget the corporate double-screw job. As far as infection goes, that's what NPCs are for, especially for the first revelation. Later, it's the PC's arse if they get caught.
Here's what I'd do:
don't make them look like aliens from the movie
don't give them a name. It's the unfamiliarity which is what is disconcerting. Let the players name it.
if you do an infection ability on somebody, use an NPC for the first time, let the PCs try to figure out what's happening (they probably will, so it's actually best to avoid this).
Simply use the humans as food for the hatchlings. The aliens grab people, and haul them to the egg chamber, where they get tied up with goo. That alone will freak out any PCs, giving the rest of the players a chance to attempt a rescue plan.
The initial contact scene should be two parties. A team of NPCs and the party (with a few more NPCs). The NPC team gets ambushed, and the PCs have to react to it (perhaps hearing screams for help). This wipes out the extras early on (less to track), and lets you present the aliens without immediate interaction with the party. The party needs to see glimpses of the alien, with examples of their power, but you want to wait for full assualt for later. You've got to herd them to a safe spot, so they can lick their wounds and come up with a plan. This also gives them a chance to witness the results of an infection (if you use that characteristic).
Maps of the facility should be available in the "safe place" If you were able to grab a PC, cut to them, showing the scary egg room, but nothing happening yet. This should drive the rest of the party to formulate a rescue plan. There should be obvious spots that look like a nesting room (and by letting the players see the trapped PC scene, they can figure out where it is). In fact, just to get this scene to happen, I would NOT have an infection ability. The players need to feel that they can rescue the PC (and having an infection ability would put the PC on the "forget him, he's gone" list regardless of how it actually works. The players should not have time and resources to fully understand the enemy, that's the point.
Once the PC's have formulated a plan of some sort, the aliens attack their position, driving them into motion (and hopefully rushing them a bit).
It would be fair to assume that the climax should be rushing to the ship, and blowing the facility up (there is blasting powder or something, right).
From there, assume one snuck aboard (hopefully a queen). The final fight should be in the loading bay (and open floor area on the bottom of the ship, where supplies are hoisted in. This should have chains and other cool ladders. The goal being, get the alien onto the chains, over the hole, and cut the chain, letting it fall to its doom (the ship being MUCH higher now).