The Neverending Story (the movie) covers only one half of the original novel. When Bastien and the Childlike Empress are holding a single shining grain which is all that remains of Fantastica (must confess, Fantasia is a better name), that's barely halfway through the novel.
It isn't even just the time-framing of the films which horrifies. Even the first movie (which is better than the others, and that ain't saying much) outright discarded most of the concepts from the book.
The whole book is about Bastion's ability to love, and this is completely absent from the first movie.
Even the fantasy elements which made the book so memorable were thrown out. This is not a complaint that Gimli's beard was 3 shades redder in the original LOTR, these are major, damaging changes. Just for example's sake, the Southern Oracle was a moving voice that only speaks and hears in verse, was basically changed to a giant statue. What? Gorgommon, Yor, and Dame Eyola were very important characters in Bastion's development as character, and Gmork was one of the most fascinating villains in fiction because he told Atreyu
the truth.
All the power and majesty of those events, such as Bastion creating bioluminescant jungle from pure thought, GONE. Bastion going from cowardly and weak to handsom, strong and brave, and the CONSEQUENCES thereof were incredible.
When I was a kid, I liked the movie, and I still think it makes a decent kids movie -- nothing on par with Holes or Toy Story, though, but in fact the book was one of the most powerful I've ever read.