Alien
I haven't seen this in so long but damn this film is so good. It's only aged in ways that make it all that much better and charming.
The atmosphere is 11/10 throughout and you can just feel the walls of the ship closing in around you and the characters the more it goes on. Music, although minimal is only there in addition to the amazing sound design. Getting to watch this on my Blu-ray copy was such a treat as it looked far better than I remembered and it was already up there.
Oh and that final 20 mins or so (MWAH)
Just. AMAZING