I'm the author of the ASHFALL three-and-a-half-ology: ASHFALL, ASHEN WINTER, SUNRISE, and DARLA'S STORY.
This review will probably contain spoilers. Read on at your own risk.
Tuck Everlasting is one of those books that I've been meaning to read. For 30 years. I've resisted until now because several people told me it was an extremely sad book.
I'm not sure what book they were reading. Maybe there's some other book called Buck Everfasting about emaciated deer that's super-duper sad. But my reading of Babbitt's book was completely different.
I suppose you could interpret the protagonist's (Winnie) choice at the end as sad. I saw it as hopeful, poignant--even beautiful. By choosing to reject immortality, she's honoring her humanity and honoring the humanness of all of us. The saddest part, for me, was the Tuck family's storyline. They never get a chance to rejoin the wheel of life, and their story doomed to never resolve.
You could read this novel as science fiction, and particularly good scifi at that. There's no question that immortality will one day be available to humans. Some jellyfish, for example, are immortal, and they're made of the same basic stuff we are: cells, DNA, and RNA. Humans have a limited lifespan because it's a survival trait at the species level. We can evolve and adapt more efficiently if our population is constantly turning over, the old making way for the young. (Imagine if immortality were currently available in the U.S., for example. The Fox News set would live and grow forever. The elderly are the demographic most likely to oppose marriage equality, most likely to be racist, most likely to be sexist, and so on. Eternal life might well spell doom for all social progress.)
So what happens when we're faced with the choice of becoming immortal? This is the moral question that Babbitt grapples with so effectively in Tuck Everlasting. And in that sense, it belongs on a shelf with much of the greatest science fiction: Dune, Ender's Game, Startide Rising, or The Windup Girl, for example. All these works grapple with important moral questions that the human race will eventually face if we survive long enough.
Also, next time someone pooh-poohs middle grade books and/or authors, buy the skeptic a copy of Tuck Everlasting. In hardcover. Then throw it at them. Hard. The writing here is lush and gorgeous--Babbitt's prose would be right at home on the literary fiction shelf. But she avoids the plotless meanderings that burden so much literary fiction. Every word here counts.
I recommend Tuck Everlasting to anyone who is interested in what it means to be human. I hope that includes all of us.