This book is heavy reading, and very academic in tone. The story starts out fairly harmless and hopeful, but devolves slowly, showing first the moral decline of those around Julian, and then Julian's own descent into egotism. While the story is engrossing, the emotional darkness, including Julian's struggle to maintain his relationship to God, makes it difficult to enjoy. Certainly there is much to learn from this book - about Mayan culture, about conquistadors, about the dangers of sailing, even about wilderness survival - but of all the books I've read for this project thusfar, it would be the hardest one to effectively sell to kids. The main character's experiences are very far removed from the concerns of most middle grade readers, and the lack of illustration and dialogue make the book look more intimidating than it actually is. My recommendation would be to read at least some of the book aloud before asking a child to read it independently. There is so much danger and excitement in the story that once kids have a taste, they will be curious to find out what happens and they will forget that the book seems old-fashioned, boring, or difficult to read.
The Captive is the first book of The Seven Serpents Trilogy, meaning that there is no definitive ending at the conclusion of this story. Julian's adventures continue in Feathered Serpent (1981) and The Amethyst Ring (1983). I did not realize this was not a stand-alone title when I chose it for my list, or I might have skipped it. I didn't enjoy the story enough to want to read the sequels, but at the same time, I'm bothered by not knowing Julian's ultimate fate. Young readers might want to be made aware that this is a story spanning three books before they start this first one.
Ultimately, this book will be but a footnote for me in the overall scheme of things. I still want to read Island of the Blue Dolphins someday, because I never have, but I have a feeling it will be a while before I'm ready to try Scott O'Dell again. Depending on how much you and your kids love long, suspenseful, and detailed history books, your mileage may vary.