"Although it is the third book of a trilogy, The Doors of the Universe stands powerfully by itself as a quest for survival on a planet that is basically alien to the Six Worlds' life forms. This is much more than an adventure story. It is one man’s realization of the need for change and his slow acceptance of the responsibility to lead that change.... This is a contemplative book, but one never gets bored with the story and it haunts the reader long after it is finished."

While this is a sequel ... it more than stands on its own as an exquisite story of the lonely quest for knowledge and the burden of unsought leadership. Noren is the archetype of the impetuous, brilliant, promising kid, prone to rebellion and despair, and abhoring the pressure and reverence alternately accorded to him--in other words, the ultimate 'different drummer' and ideal adolescent protagonist. The technological, social, religious and philosophical landscape of the planet is carefully depicted, but not overly detailed, thus giving pleasure to voluntary readers and meat to creative teachers of English or Social Studies.

"The last few chapters become compelling, showing a power and mythic 'rightness.'"

"This book and its companions, This Star Shall Abide and Beyond the Tomorrow Mountains, will become classics of science fiction. They will not, unfortunately, be popular [with young people] because the intellectual level and reading difficulty will restrict their circulation to the more intelligent high school students.... I admire the care and precision with which Engdahl has worked out the limits of the environment of this alien world, but especially the careful delimiting to its morality: what is in the best interests of the long-term survival of the race. Right up to the end of the book I had no clue as to the brilliant way in which all the problems raised would be resolved. And that makes a good book!"

"This Star Shall Abide and Beyond the Tomorrow Mountains ... serve as solid foundation for this powerful culminating volume that treats in far greater depth the philosophical/ethical/religious issues raised in the earlier books.... Almost as much a character study (albeit of a very special individual) as science fiction, Engdahl's latest story is certain to appeal to the thoughtful good reader. High school."