Which books have been worth an initial struggle?

[Cait]

Initially, Mobius_Walker was overwhelmed by Rebecca Roanhorse's pre-Columbian inspired science fiction fantasy, Black Sun. "I ended up loving the characters (especially Xiala and Serapio), so I will definitely be picking up later entries in the series." Which books have been worth an initial struggle? (Cannonball Read 13)

[Raven]

Most books in the end are worth it. At the very least you come away with an understanding of what you might not like in a book. However, RASL was one of the first books that made me mentally feel ill (almost to a physical level) and yet, I have never read something that I thank so hard for hitting me between the eyes.

[Robert]

Ann Leckie's "Ancillary Justice" was a hard one to get into due to the style and world building. So was her "The Raven's Tower". But worth the initial struggle.