Character-based complexity is underrated. A novel with a huge cast of similarly named or minimally differentiated characters, like some epic fantasies or Russian classics, can be a nightmare to keep straight. You spend more time flipping back to the 'List of Characters' at the front than you do actually reading. The complexity isn't in the ideas or prose, but in the basic tracking of who is who and how they're related. It's administrative complexity! A family tree or a map shouldn't be a mandatory accessory for basic comprehension, but for some books, it absolutely is.
Honestly, sometimes the most complicated book is the one written in perfectly clear prose about a subject you know nothing about. Picked up a hard sci-fi novel once that assumed I had a physics degree. The structure was simple, but I was lost by page three. Complication isn't always in the telling; sometimes it's in the sheer density of the imagined world.
Don't be afraid to read things out of order sometimes. With something like 'Infinite Jest,' I ended up reading the endnotes as their own separate mini-book before integrating them.
I'd read a chapter in the main text, then flip to the corresponding endnotes and read them in a batch. Trying to constantly flip back and forth in the physical book shattered my concentration. Treating the footnotes/endnotes as a secondary, supporting text I could consult on my own terms made the core narrative flow much better.
It felt like cheating at first, but it's my book and my reading experience—I'll structure it in the way that makes the content most accessible to me.
It constructs a maze where the walls are made of concepts instead of brick. You're not just lost in plot twists; you're lost in epistemological doubt or ethical paradoxes. The 'action' might be a character sitting in a room thinking for thirty pages, and the tension comes from whether their logic will hold or collapse under its own weight.
This demands a reader who finds pleasure in that kind of strenuous mental exercise. The reward isn't a thrill, but a profound shift in how you see something—a door in your mind creaking open that you didn't know was there. The book becomes an event in your intellectual life, not just your reading list.