The book is of course GR bible Gravitation by MTW.
https://www.amazon.com/Gravitation-Charles-W-Misner/dp/07167...
That's too general a statement. You're certainly correct that a engaging consistent story with good characters is much harder than, say, the average cookbook or travel guide.
But many textbooks in science and math seem like absolutely Herculean effort. Surely, Gravitation[1] by Misner, Thorne, & Wheeler or The Art of Electronics[2] by Horowitz & Hill (both non-fiction) are equivalent in intellectual effort to all ~5000 Harlequin Romances (fiction) put together.
[1] https://www.amazon.com/Gravitation-Charles-W-Misner/dp/06911...
[2] https://www.amazon.com/Art-Electronics-Paul-Horowitz/dp/0521...
I certainly enjoyed the movie, and I really loved the visualizations of a wormhole and of the large spinning black hole, things you usually have to imagine as a physicist without ever seeing with your eyes.
[1] http://www.amazon.com/Gravitation-Physics-Series-Charles-Mis...
long story short, gravity is the curvature of spacetime. objects of mass cause the curvature, and the curvature in turn causes objects to move locally along geodesics (shortest-distance paths), which causes the curvature to shift
when you throw a ball and it's moving through a parabola, that curve taken with time in a riemannian space is actually the straightest line possible from one end of the throw to the other
this is Einstein's magnum opus General Relativity
Nice to meet the unicorn! Meanwhile, how many textbooks are on the shelves at Barnes&Nobel? Not exactly bestsellers, right? Even the University of Washington bookstore puts the textbooks in a separate room in the basement.
> Textbook-level treatment of a subject is usually very shallow
Maybe the ones you read are. The ones Caltech uses aren't, like this one:
https://www.amazon.com/Gravitation-Charles-W-Misner/dp/06911...