The Strange World of Planet X (The Cosmic Monster, Cosmic Monsters) is a 1957 British science fiction film starring Forrest Tucker. Sigh... Yet another voice-over narration gets us started. "Man goes forward into the unknown, but how does the unknown react?" A theremin is used to provide some of the music. I wasn't expecting much from this one, but I ended up liking it. I liked Forrest Tucker. I wonder why this film is so little known? Other poorly received movies have fared much better while this one has languished by the wayside. I may be all alone in liking it.
Googlevideo has it online:
TCM has an overview, but this is another one I'm having trouble finding reviews for. There's a review here. DVDTalk says it's "a notably inconsistent and dramatically unsound jumble of ideas" and "has no momentum and characters that aren't very interesting".
2/20/2009: Classic SciFi Movies has a review.