Forbidden Planet is still a great movie today. While This Island Earth is a bit more dated and scientifically implausible, it is also a good movie.
As for production of B movies, the 50s were unparalleled, with classics like Them and The Monolith Monsters.
And it was when the Japanese got started with Godzilla and The Mysterians.
A good decade.
Forbidden Planet was the first big budget SciFi that was shot in color.