Alien (1979)
Notes
One of the most influential sci-fi horrors. Even if you don't know Alien, you do know Alien.
Review
A personal favorite of mine. Any time I rewatch it, I find that it's a little bit slower-paced than I remember. The horror here really is off the general premise. The Xeno is not bad, bless the use of costumes and such. It holds up better as the years go by than any of that early CGI trash. But those jazz hands do take me out a bit. Even if the scene prior (Dallas in the vents) is wonderful with how tense it gets.
The sheer banal evil of space is an interesting position. And it's excellently told with a devotion towards characterizing these silly little folks that are about to get offed one-by-one. Space truckers! I love it. In addition, the actual aesthetic of the whole Alien enterprise is one of my favorites. I love that we're well in the future, but we're still using green screens and tapes. It feels so much more like a place than many of the sleek and shiny futures I've been shown. It feels lived in.