It would have helped if for the part of the alien Klaatu they hadn't cast an actual alien.
Of the science fiction films from that era there's always three I go back to; the aforementioned Day the Earth Stood Still, Forbidden Planet, and This Island Earth. There are a host of others I enjoy from that time period, but not as much as those three.
Incidentally, one of the X-Files producers directed a film a few years ago which is sort of a homage to that period/genre of sci-fi. It's called Alien Trespass. And while it doesn't have the same charm as the originals (or the cheesiness) it's a nice nod to those old films. Just a pity it wasn't shot in black and white.