Is that there are two superior actors in major roles; Patricia Neal and Sam Jaffe which is rare in sci-fi, not to mention a good director in Robert Wise. The only other sci-fi film that i can think of with 2 top actors is Them with Edmond Gwen and James Whitmore. Maybe Spencer Tracy and Ingrid Bergman in Dr. Jekyll and Mr. Hyde (1941) but i don't call that a strict sci-fi, there's other things like psychology and social norms involved.
shareOn a side note: Spencer Tracy tried out for the part of Klaatu, but Wise intentionally gave the role to a (then-)newcomer and first-timer, Michael Reenie. Wise wanted to convey the character with someone the audience had never seen before instead of possibly losing the character if the viewers saw the legendary Tracy instead of the character, see.
Though everyone knows of the tremendously effective acting ability of Tracy, I think that was nonetheless a very wise idea on the behalf of the great filmmaker Robert Wise.
--
StrangerHand: Now 75% more afro-free!