An interesting flick that, unintentionally, affirmed some racial stereotyping and danced with some then taboos ("miscegenation," end of monogamy, etc).
Also, given the cause of human annihilation, it was impossibly hygienic. Movies like "The Ultimate Warrior" and "The Omega Man" showed the human detritus far more convincingly. Then again, such images were socially impossible to portray in a 1959 theatrical film.
It was sincere, however, and the performances were good.
And it didn't hurt that one of the loveliest (and sadly fated) actresses of the next decade, Inger Stevens, was its leading lady.
If you've not seen it, I would recommend it if you allow for the times in which it was made.
TVAG