Unlike some literary criticism, this book was fun to read. Instead of getting bogged down in tedious interpretation debates, Green simply tells the story of space travel in science fiction with just a touch of humor. He mentions works that are quite forgotten. In addition, there is a section at the end where he talks about "Out of the Silent Planet" and "Perelandra". On the whole, if you are interested in the science fiction of the past, I would definitely recommend this book.