Women of the Prehistoric Planet (1966)

How bad is it? It's a cavewoman, science fiction film with John Agar. Nuff said.
Should you see it? Sure.

John Agar and Wendell Corey are astronauts who land on a planet of cave people and stock footage giant lizards and a giant spider. There's a "surprise" ending I don't feel bad about spoiling - they name the planet "Earth." Also in the cast are Stuart Margolin, Lyle Waggoner and Merry Andrews, who is the sole woman and not from the prehistoric planet.