Decent and brisk science-fiction movie, set in 1973, about the White race's obsession with manned exploration combined with the sheer terror of what they imagine they might find on their travels. Almost as if the 'final frontier' were somehow analogous to the "Dark Continent" of Africa.
The "it" here comes very much from the Caucasian id, especially given the fact that this space mission is actually a military exercise undertaken by the 'United States Space Command' in a rocketship packed-to-the-gunnels with military ordnance - automatic pistols, carbines, fragmentation & gas grenades & a bazooka. Quite an arsenal for a round trip to a supposedly-dead planet like Mars!
Surprisingly technically-accurate - at least in view of the silence of space necessitated by the fact that sound, unlike light, does not travel in a vacuum - this movie has too many characters to emotionally invest-in. But at least none of the actresses are here to shrilly scream for the men to come and save them since they actually perform scientific functions in the plot and are treated as more-or-less equals by the men.
The horror element is less successful here since "it" is clearly just a well-built man in an ill-fitting monster suit - whom walks stiffly just like a well-built man in an ill-fitting monster suit would - partly-hidden behind a gloomy lighting-scheme.
What really hurts this movie is that the creature has no motivation for its behaviour beyond wanton destruction and dealing-out death; making it the unreasoning creation of irrational cinematic minds whom are unwilling to grow-up beyond childhood stories of bogeymen.