When I trace the contours of dark fantasy that really lingers, my mind goes to writers who shape mood like weather. China Miéville's prose can be baroque and yet icy; in books like 'Perdido Street Station' he builds cities that feel like living nightmares and then refuses to explain everything, which leaves you strangely satisfied and unsettled. N.K. Jemisin, especially in 'The Fifth Season', combines emotional depth and inventive worldbuilding so that the darkness comes from systemic cruelty as much as from monsters, and that makes it hit differently.
I also find Mark Lawrence's 'Prince of Thorns' trilogy and Joe Abercrombie's 'First Law' books irresistible because they braid moral ambiguity with sharp, often sardonic voice. Glen Cook's 'The Black Company' remains a masterclass in telling grim stories from within the ranks — it feels intimate and bleak without melodrama. For something more dreamlike and uncanny, Jeff VanderMeer's 'Annihilation' and M. John Harrison's quieter, philosophical works are tiny knives that cut deep. Female authors like R.F. Kuang with 'The Poppy War' and Angela Carter’s fairy-tale revisitations offer dark fantasy that interrogates power and trauma in ways that stick with you long after the last page.
If you want the most beguiling dark fantasy, pick a book that unsettles both your expectations and your sympathies; I love it when a story stains my imagination and refuses to wash out, which is my high bar for the genre.