Most folks who've watched this and Alien see the obvious similarities. In fact, Alien is what we all kind of imagined as kids watching this film and seeing it with the non-critical eyes of youth.
Regardless, this is a top drawer B movie effort that rises far above its limitations with solid acting, a fine story, eerie and claustrophobic settings with effective lighting, a quick pace and no lag-time.
If you haven't seen it, get the MGM Midnight Movie DVD double with Monster that Challenged the World, another superb B Movie sci-fi thriller that is as good as this one, and has an insect-like monster that you might recognize as the forerunner of the giant bug of Men in Black.