As Bruce is drifting in and out of consciousness across the book, he's plagued by haunting visions of Enchantress, who seems to have infected Bruce's childhood memories and perverted them. And although they're written with extreme precision that makes them intimidating, the way they're scattered across the book throws the main story out of sync.
Are we supposed to be hunting The Joker's killer or chasing Enchantress down the rabbit hole of Bruce's brain? Because both of those concepts are fascinating, it's hard to be invested in both wholeheartedly.
Once the narrative snaps into the flashback, the reader becomes invested in the sub-plot, but when it's snatched back from us as Bruce jolts himself awake, it's annoying. Like an infuriating jigsaw puzzle that just won't fit together properly. And on the reverse side of that, the main plot is enthralling, but frequently breaking away into a flashback feels like a lazy way of spreading the mystery out.