The Cosmic Man (1959)

It begins in the usual manner, with a blip on a radar being observed by someone in a small room, followed by the military and scientists all trying to figure out how to get into the alien ship. But it then continues to be familiar, borrowing liberally from the plot of the much better The Day the Earth Stood Still, which came out eight years before. It does an okay job with it, to be fair.
The visitor is kind of creepy, even if his motivations are somewhat vague. And the slow but short (just 72 mins) script has some interesting content, such as tantalising the audience of the day with crazy scientist talk about anti-gravity.

2½ manifold purposes out of 5