Dark Star is very good. The scenes with the big inflated beach ball creature are pure slapstick and I enjoyed the conversations where they tried to get the intelligent bomb to return to the bomb bay.
Forbidden Planet is another good film. The special effects are basic but effective with the invisible monster crashing into the force field and creating foot prints. The security screens slamming into place over the windows of the building was an extremely simple effect but it really worked. I found the whole story line with the Krell innovative. Quite a hard film to beat.
Enemy Mine is another old but good film. A human and an enemy alien learn to overcome differences. As I recall the special effects were very ropy though I found the alien itself well done. I think the film can be seen on several levels.
There was another firm with that had a human surviving alone on Mars doing things like living in caves and heating rocks to release oxygen. It was a predecessor to the recent The Martian starring Matt Damon, the name of the original film escapes me though (maybe I am confusing things with Enemy Mine).
Among the newer films Alien has to be mentioned and I though Predator was great for depiction of the predators themselves. Terminator was a lot of fun.
