Full disclosure: I never bothered to read anything of his written after "The Moon is a Harsh Mistress", since the universal consensus seems to be that his later books are very, very strange.
He had a blocked carotid artery for several years, and I some Heinlein fans blame his crazier stuff on that.
I think his later books are just what happens to many successful creatives. They get so famous that no one else has any editorial control over what they produce, and the quality of their work decreases.
