I see Jerry Goldsmith as a big, important part of the Alien movie's functionality. The Alien soundtrack is great, and the "Alien complete soundtrack" released in 2007 is really interesting in my opinion, it has tracks that Ridley Scott rejected from the movie due to their dynamics. I recommend listening to that through.
In terms of the functionality and atmosphere of the Alien movie, Jim Shields' contribution to the movie is often forgotten, or I think not everyone even knows about Jim's contribution to the movie. Shields made the background sounds for the scenes, what can hear in the movie; hums, beats, crunches, clicks, etc. Without these, the atmosphere of the movie would be something completely different.