The Quatermass Xperiment

A British spaceship returns to Earth but instead of celebrating this first space shot, there is a lot of confusion, as two of the three crew members are missing. Additionally, the one who DID return just doesn't look or act right and he's kept under supervision and monitored as his body seems to be undergoing some sort of metamorphosis.

This isn't exactly your standard 1950s sci-fi/monster film, as the story itself is more tightly written and seems more credible than the typical "bug-eyed monster" film. Instead of the over the top acting and silly special effects, this is a more cerebral style film and the "monster" doesn't even make an appearance until near the very end. Instead, the story slowly unfolds and at the same time, simple makeup does the trick--no ping pong ball eyes, giant killer lobsters or any of the sort of tripe seen in the sillier examples of the genre. About the only negative was the whole subplot of the wife trying to kidnap her husband away from the hospital--this didn't make a lot of sense. Still, overall it's a dandy sci-fi film and worth a look.