Start with The darkness that comes before. It is the first book of The Prince of Nothing, and the most common mistake readers make with this series is treating the two sub-series as two front doors.
They are not. The Prince of Nothing — The darkness that comes before, The Warrior Prophet (The Prince of Nothing, Book 2), The Thousandfold Thought (The Prince of Nothing, Book 3) — comes first and is complete in itself. The Aspect-Emperor — The judging eye, The White Luck Warrior, The great ordeal, The Unholy Consult — opens twenty years later and assumes you have read the first three. It does not recap and it does not reintroduce; its opening chapters are deliberately disorienting even for readers who have. Books one to three, then four to seven, and the boundary between them is a continuation, not an alternative start.
Content, stated plainly
Bakker's books contain sustained and graphic sexual violence, most of it against women, and it recurs across all seven volumes rather than appearing once. Readers divide genuinely on what it is doing. One reading holds that the series is an argument about domination — that its world is built on the premise that people are largely automata running scripts they did not write, and that depicting the brutality of such a world without flinching is the point, with the prose withholding any sanction for it. The other holds that the sheer volume and specificity of it exceeds anything the argument requires, that the female characters are disproportionately defined by it, and that at some point a critique of degradation that dwells this long becomes the thing it claims to examine. Both readings are held by serious readers of the series and neither is obviously wrong. Know that the argument exists before you commit to seven volumes.
The Prince of Nothing
The darkness that comes before is roughly 589 pages and opens with a prologue of monastic training and about a hundred pages of unglossed vocabulary before the plot engages. That difficulty is the series in miniature rather than an accident, and readers who reach the assembly of the Holy War rarely stop. The Warrior Prophet (The Prince of Nothing, Book 2) is the march itself, where the First Crusade parallel becomes explicit and brutal; it and book one were written as one manuscript and the split is arbitrary, so read them back to back. The Thousandfold Thought (The Prince of Nothing, Book 3) closes the first movement and answers what Kellhus actually is.
The Aspect-Emperor
The judging eye jumps twenty years with the world remade and no explanation of how; its descent through Cil-Aujas is the best single sequence in the series, and it only lands if you already know these characters. The White Luck Warrior separates the plot lines for good and functions as one volume with its predecessor. The great ordeal was originally half of a longer manuscript split by the publisher, which is why it ends where it does — it and The Unholy Consult are one book, and stopping between them is the worst possible pause. A large share of readers actively dislike the ending, and the story is not tidily concluded: a further series has been announced for years and has never appeared.
Where to stop
The Thousandfold Thought is a legitimate stopping point. It closes the trilogy properly and leaves you with a complete story. Stop there if the first three have exhausted your patience, because the second series is longer, harder and ends without resolution.
The crusade underneath it
The First Crusade: A New History by Thomas Asbridge is the most readable single-volume account of the campaign the Holy War reproduces — the preaching, the famine at Antioch, the massacre at Jerusalem — and about 448 pages. Read it after The Warrior Prophet (The Prince of Nothing, Book 2) and watch Bakker track the historical sequence event for event before twisting one thing. Christopher Tyerman's God's war is the scholarly history of the whole crusading movement at roughly 1,000 pages; take it second, and only if the first one leaves you wanting the why.
Bakker outside the series
Neuropath is a near-future thriller stating outright the neuroscience argument the fantasy dramatises — that the self is a post-hoc story the brain tells. It is unpleasant by design and much shorter than anything in the main sequence. Disciple of the Dog narrates a detective novel through a man with total recall who therefore cannot revise his own memories, and is the lightest thing he has written.
For context, Shadow & Claw — the record collects the first two Book of the New Sun volumes, which is how they are normally sold — is the obvious ancestor, and The Blade Itself is the other pole of the same moment in fantasy, the same disenchantment played for comedy instead of philosophy. The full ordered sequence sits on the Second Apocalypse reading path.