One thing about Aliens that I liked a lot are the Aliens' abilities to attack from the ceiling and jump off walls. And the speed of the one that nearly gets Hicks and Ripley in the elevator was great. But there was certainly quite a bit of buildup between attacks. Not as much as in Alien, but enough, like Hicks pushing the elevator button and them waiting... So excruciating!
I think a huge step is the music, though.
Personally I think the Alien: Isolation team knocked it out of the park with their music. Just amazing stuff:
http://www.youtube.com/watch?v=CeunRV9LE90#wsAnother great example of that spooky ambiance I think Alien 5 needs is the Doom PSX OST:
http://www.youtube.com/watch?v=GV5UnANIj3c#The right music married to the right visuals, with a good pace to the visuals, with moments to soak in the dread, essentially will carry the film. The actors themselves need not be complex, but convincing (realistic dialogue like in Alien, instead of the scripted Prometheus-style dialogue). The set needs to be peopled with believable characters. Not big-name thespians reading their lines in bombastic fashion.
If these conditions are met, the story can be kept minimal. No explanation needed when you see the Space Jockey. : )
Edit: Of course, the original score for Alien in its complete form wasn't released until after Jerry Goldsmith's death. I think it was released in 2010, but I could be wrong. In the original firm, the opening was rewritten, and the ending replaced with Howard Hanson's Romantic Symphony (imo, the best ending theme of any science fiction film, ever). Also, the film's editor, Terry Rawlings, listened to Jerry Goldsmith's Freud while editing the film (which was silent as a workprint). The music worked so well that they used it during the acid test, and while Dallas is in the vents.
I think Jerry wanted his score used unchanged, but Scott happily cut it into little pieces and used it when he felt like it. Some of the best scenes have no music at all, but instead have ambient sounds: breathing, heartbeats, and machine noises. Some scenes, such as Ripley undressing, are almost complete silent except for sound effects. Or, the crew in the Derelict, with the only sound being heard are their helmets. The lighting of that tunnel is so incredibly and eerie when all you can see are the shadows of the space suits, hear the breathing of the venting helmets, and nothing else. Pure audio/visual bliss.
Of course, the score itself featured a lot of unusual instruments, or instruments played in strange fashion. That weird wind sound that occurs several times, such as during the opening scene, which the makers of Alien: Isolation later dubbed as the "space whale." I'm hoping the sound guys for Alien 5 tap into that. Create bizarre otherwordly sounds that will drive our imaginations crazy. And for God's sake, keep the movie dark! The reason the first film works so well is it's not what you see, but what you think you see. And once you start hearing things, your mind plays tricks on you.
On a different note, one of my favorite films of all time is Halloween. In it, JC loved to have the Shape in the foreground and background with the other actors unaware of it. I can't remember if anything like this happens in Alien or not, but I remember the medic in Aliens saying "Maybe they don't show up on infrared at all!" before the alien warrior climbs out of the wall and grabs her. The shot works very well -- and the Shape in Halloween worked so well -- because there wasn't a cut. We're given time to dwell on what we're seeing, like an evil magic eye that kills you when you solve it. I hope Alien 5 has minimal cuts and long takes. Alien did, much to its benefit.